now I remember... nah, stuff like Insanity is way better.

Until an insane enemy attacks and kills one of your characters, despite being insane.

I prefer things like paralysis, as such enemies can't act at all.

Or Toxic Cloud, which has a chance of re-applying status ailments every round.

Or, at high levels, multi-target instant death. At a low power level, it's a nice way to thin out crowds of low level enemies, especially when those low level enemies have high HP.

Prismic Ray/Chaos and Pandemonium also have the problem of causing undesired status ailments sometimes. You might inflict fear, which tends to prolong the battle by making enemies run away, so you can't kill them as quickly. Prismic Ray/Chaos can also inflict slow (enemy animations take longer) or turncoat (can't attack the enemy while it lasts, and once the other enemies are dead, the turncoat will wear off, causing you to fight another battle).

But it still makes things take longer when I could have just killed the enemy in the previous fight, plus with Prismic Ray/Chaos it could easily be more than one enemy, especially since some of the enemies may have run away due to fear/blindness.

At this point in the game, it isn't whether the party can handle the enemy, but rather how quickly the party can get past the encounter. Survival is only an issue in the earlier part of the game; by the time those 6th level spells come into play, that's no longer an issue.

(The game, unfortunately, has an inverted difficulty curve from Arnika Road onward.)

I'm one of the very few W8 players that actually enjoys the grind (to a point; we all have our limits.)
I've been patiently grinding my MDP's skills, trying to get all their magic realms all the way to 100 skill. Their main spellbook skills are all maxed by now, even the Priest with his mediocre Piety (the only controlling attribute for Divinity) has finally reached 125 Divinity. The realms are all 97 or better by now. This takes a lot of time, spreading out the realms each round to try to train everything, resting when SPs run out, etc. I haven't ignored the Bard and Gadgeteer either; their Music and Engineering skills are at 97 and 98 respectively.
I also take the time to patiently get their melee skills respectable, by that I mean at least 50 to everything so they get that extra swing or attack, or whatever the 50 skill breakpoint does. IMO melee is the most annoying to train for an MDP because that's what the party is worst at. Not only that, but by higher levels, a lot of enemies won't close with you to short range. This makes magic and ranged combat much easier to train.
My favorite guaranteed melee training spot is the rat room (the no-magic library in the Upper Monastery). If enemies DO spawn in the UM after a rest (seems to be random), then melee-only rats WILL spawn there. This is the perfect opportunity to swap out my Bard/Gadgeteer/Priest to the front rank by themself to use their melee weapon and shield, protected by Guardian Angel, to smack rats down, one by one, until they're all dead. There is a narrow hallway just before you get into the library (a sweet spot) where you can still use your magic, and the rats can only hit the one party member in front.
Sometimes you get really lucky and get 9 Pestilent Rats (that is a ton of weapon smacks; death by 1,000 cuts), especially for the Priest, who is only hitting for average damage with his 45 Strength and War Scepter, with its whopping 3-8 listed damage (at least it doesn't have a negative modifier to To Hit or Initiative). Doing this, my Bard and Gadgeteer raise up Close Combat, Sword, Shield, Powerstrike, and Reflextion skills all at once. My Priest raises his Close Combat, Mace and Flail, and Shield skills.
The reason for this melee training is that some enemies will be resistant, or practically immune, to magic later on. I anticipate being surrounded by various bats, and Juggernauts/Piercer Modais on the AT Road. In Arnika, tougher Savant Berserkers/Slashers will try to surround your party, as well as the toughest Savant Minion, who can hit from extended range, and possibly paralyze.
This is why maxing Piety for Iron Will makes sense; not only does it raise your resistances to each element, it protects against side effects of physical attacks as well. At least for my 4 specialist casters, this makes sense to me. Piety grants spell points in each realm, extra stamina, and Iron Will at max. Iron Will would be nice for the Bard and Gadgeteer, but for them, it seems too costly, as they don't even get spell points from Piety, only stamina (which you can also get from Strength and Vitality). Piety is also a controlling attribute for every realm.
DTGreene, you are right about level 6 and 7 spells. I'd say about half of them are good. As I said before, I force myself to pick a spell every level up, no saving spell picks. Obviously, I pick the ones that benefit me the most first. Failing that, I pick a spell that I will never use, but that gives extra spell points to a realm lagging behind. I find that, at least in the Lower and Upper Monastery, Fire and Mental realm skills seem to be the best against various slimes, rats, bats, seekers, and Higardi Bandits.

whoa... as someone who ironmanned wiz8 several times, including once or twice on expert, psionic might be my favorite class. one word: pandemonium, power level 1-2. a bard using the instrument can’t really control the power level iirc, whereas a psi can spam mini pandemoniums, disrupting and controlling the battle as needed. the fact that pandemonium cannot be resisted is just awesome, you can’t really land normal crowd control very well against most high level monsters

that, plus mental immunity is really nice, and, psionic fire has the most efficient mana to damage ratio out of any fire spell. at least, in wizardry 7 it does, and i seem to recall it requiring the exact same mana in 8.

(they also get silence, which is pretty good)

The problems I have with Pandemonium are as follows:
* Early/mid game: This spell can't be cast, as you're not yet level 14. While you can use it via Pandemonium Power, that item, like way too many of the consumables, is probably more expensive than it should be, and i would be better to sell it to get better equipment and/or spell books instead of actually using it.
* Late game: You can actually cast the spell. Problem is that, at this point, status ailments aren't as useful due to enemy resistance, and aren't that important because the game isn't that hard anymore at the point that you get access to Pandemonium as a spell. Furthermore, since this spell inflicts fear, it will make enemies run away, which tends to make battles drag on longer than they would otherwise.

Thing is, by the time you can cast Pandemonium, you are beyond the point in the game where there's a real risk of losing a battle, and are at the point where you want to win battles faster, and Pandemonium's fear effect makes battles take longer, which is the opposite of what you want at this point.

(Note that lower level spells that cause fear or blindness have their uses because you're still worried about the risk of losing a fight, so taking extra time to win isn't a big deal; by the time you can cast Pandemonium, there's little risk of loss, so prolonging a fight is not a good idea at this point.)

I see what you’re saying, although
1) Pandemonium Powder has singlehandedly saved parties in the low and mid levels. I remember a couple games where some random plants and bats joined in and I was surrounded. In ironman games I always had a dedicated throwing guy for stuff like pandemonium powder / ice bomb. Although admittedly I did sell some powders each game, I always had at least a few on hand
2) I do recall at least a few high level battles where Pandemonium, the spell, was more than useful. The battle with all the cultists and giant skeleton guys, the casters were feared allowing me to focus on the skeletons. Also there’s a huge battle near the end of the game with a ton of casters in the distance where it helped out.

The fact that they can’t be turned insane or charmed also makes them a pretty resilient support.

Is Psi amazing? No, but I never felt it was as bad of a class as people said, and Pandemonium always felt like a good safety net in case things ever went wrong.

There's other spells that can be useful in many of those situations at high levels:
* Freeze All, from the Wizard list, targets all enemies with a status ailment and doesn't have the same issue of prolonging the battle. Also, I note that this spell can work on undead.
* Psionic Blast, from the Psionic list: While it only hits a group, is a great spell for dealing with enemies that aren't close; it's the only damage spell that can hit through walls, not to mention that in can inflict insanity without a risk of inflicting fear and prolonging the fight.
* Quicksand, from the Alchemist list, can kill enemies outright. It and Resurrection are probably my favorite level 6 spells, and if possible, I always choose these spells first. (Might to Magic is a nice fun spell, but it ultimately isn't that useful, though at least it's better than Lifesteal.)
* Many of the spellcasting enemies, like Cultists, have low HP. If you can blast them with damage spells before they can put up a barrier, you can kill them before they can cast too many spells. Also, Eye for an Eye can cause them to be hit by their own spells, which can often end up killing (or disabling) them.
* If you can get Silence to work, you can force the cultists to charge at you, I believe, and they're easy pickings in melee. Unfortunately, I haven't found that spell to work that reliably. (Also, the Silent Lyres are too heavy for a spell that niche and low level, and why are there 2 of them?)

(Note that, of the spells listed, Bards can get access to Freeze All (and Freeze Flesh), Pandemonium, Lifesteal (which is decent on a bard considering the lack of good offensive instruments), Silence. Gadgeteers don't get access to any of these spells, but they do eventually get Asphxiate, but you might want to be careful with that gadget if you're playing Ironman.)

(Notice that my objections apply specifically to effects that can cause fear or blindness, like Pandemonium and the Prismic spells, not to Psionics, who still have some handy spells like Psionic Blast.)

Right, but the problem I had with standard crowd control was that, by mid game, monsters start resisting 95% or higher. Like I remember spamming Freeze All during some of those ridiculously huge Rapax battles in the Rift, just to speed up the combat, and each time, maybe one or two Rapax would get frozen. Same with Quicksand. Still helpful, yes, but more useful for thinning herds as opposed to giving you some breathing room.

(It may be the fact that I was playing on Expert, maybe the monsters have higher resists there, it’s been awhile since I played Wiz8.)

But yeah, I do agree, enemies running away—prolonging already absurdly long battles—isn’t any fun. xD

This is why my MDP is ignoring spells like Blizzard (causes blinding), Pandemonium (causes fear), and the Prismic Ray/Chaos spells (causes whatever, including enemies running away).
My Psionic is about to get level 27, as a Human. This gives enough points to max Speed, Senses, Piety, and Intelligence (with help from the Trynton fountain +5).
This means that, hanging out in Arnika with the good enemy spawns generating 100K experience each, Snakespeed (already at 80+ for +5 initiative), Eagle Eye (great for sling users), and Iron Will (great for anybody) can be unlocked by level 27.
The other "useless" Psionic attributes (Strength, Dexterity, and Vitality) are at 45 minimum, as a Human. They will never be maxed, so putting +2 into each at level up is the balanced way of doing things.