A lot of what you mentioned above looks good in theory but in practice it isn't necassary but it depends on your party composition. My party front liners always have str dex and con all at 18, if this was not the case then maybe some of the buffs you mentioned above would be more useful. Later in the game, my characters usually had good weapons and armour that stacking buffs was just overkill. This was on normal, hard and insane difficulties too.
Protection from evil, prayer, recitation, the AOE prot from evil spell were not needed because my parties were just as effective without them and this is why I lumped them in with the trash spells but maybe I shouldn’t have done that. Some of them are useful but only for certain battles; you didn’t need to have them active all the time and you certainly didn't need several castings. Entropy shield might be a good buff but heal is the spell you should be using at that level. I also stick with what I said about all level 7 clerics spells being crap, symbol of hopelessness is such a crap spell for such a high level. Instead of casting a save or else spell, why not cast a few summons which are all but certain to distract the enemy? The summons don’t need to be a particularly high level either. Hell, if you want to halt the enemy, the 3rd level Animate Dead spell is a better option, and it works against undead too. Why leave to chance what you can control directly? Flame strike is also garbage, long casting time with high possibility of enemy moving out the way (or getting killed before the flame hits) makes flame strike one of the more useless direct damage spells in the game. Also flame strike as a troll killer is like killing an ant with a sledgehammer, just plain overkill. A wizard’s burning hands spell (or druid’s sunscorch) is much more efficient. There’s also more than enough weapons that do fire damage making troll killing spells a convenience at best.
The fire protection spells were something I hadn’t considered though but that’s because I tend to use fire elementals and bomb them with fireballs when the enemy closes in. Fire protection gear wasn’t exactly rare either but I never tried buffing it with spells. Next playthrough that is something I will try..
kmonster: I disagree about the multclassing of primary cleric, druid and mage (thieves don't loose anything important by multiclassing).
Even the party cleric helps more pure classed than multiclassed during the game.
Really? Because my experience was exactly the opposite. I did use a single class cleric in my first 2-3 playthroughs but found using a multi was much more effective. Since that discovery, I never looked back
Mages on the other hand are different, they should be specialized as the extra spell per level is usually worth the loss of 2 spell schools (sacrificing necromancy, evocation and conjuring is a big no no though). Necromancers for example only lose one good spell, mirror image. If you want a single class generalist mage, the bard is a better choice.
kmonster: Extra healing spells do make a difference, reducing the need for searching a safe place to rest and you'll be happy that you don't have to wait another level when a party member died deep down in the dungeon.
When your fighter is in trouble healing over 100 HP during combat from the distance using the resurrection spell can be a lifesaver.
No they do not, potions fill that role just fine without wasting spell slots on healing spells. Also, healing potions are in infinate supply, they are always available. If your fighter is taking 100 odd damage and needing resurrecting, then maybe he should be getting assistance from the other party members and you should be adjusting your tactics. If the resurrection spell is part of your tactics then you’re doing something wrong. Party members shouldn’t be dying, period.
kmonster: An extra level in chapter 1 helps turning the many undead there and even in TotL most of the undead are turnable, you won't note it with a slow leveling multiclass however.
Turning undead in chapter 1 causes them to run behind spell casters and regroup with forces behind them. I remember 5 spots where that can happen. It’s better to draw them out, bottleneck them then take them as that scenerio can be predicted and controlled. Turn undead leaves quite a bit to chance.
The undead in TOTL (the part where you have to put 4 scrolls in the 4 sarcophagus right?) die so fast anyway that turn undead isn’t even worth considering. When the crypt thing’s teleport your party members to a random area, meeting back up with them is still never a problem. By the time a cleric attempts a second turning, the front liners will have already cleared the enemy and started moving to the next area.
I am aware that at higher levels, turn undead can destroy them outright which might be good in HOF mode (I haven’t tried it yet so I can’t say if it’s the case) but in non HOF mode, characters aren’t high enough level so turned undead just end up running around, potentially putting them in areas you aren’t ready to go yet (like places with spell casters and traps). I still say it’s better to control their movements than leave everything to chance with turn undead.
kmonster: Let's do a comparison between pure class cleric and multiclass cleric near the end of chapter 2 when it gets difficult.
It's only a level (7 vs 6) but this does make a difference.
The abilty to cast "Protection from Evil 10' radius" alone is enough to even out the fighter benefits, it grant +2 to AC and saving throws to all 6 party members for a long time. But you also get another level 4 slot to cast defensive harmony or recitation for further improvement. A casting of the Animate Dead spell will summon one extra undead level, a prayer will last longer, ...
In a combat oriented game, I fail to see the logic in sacrificing fighting ability for the entire game for earlier access to the paltry Protection from evil 10’ radius spell. I suppose it might be good if are getting hit more than you should but instead of dragging out the battle with Yxonemei with a level 4 defense buff, using a useless offensive character and still take a whacking, you can use the level 3 animate dead summons to distract her and use attack buffs to end the battle quicker, taking fewer hits in the process thus making the 4th level buff unnecessary. The best offense is not a good defense. Ever consider that maybe your emphasis on buff duration has more to do with poor damage output rather than the importance of a single class cleric? Without seeing your party, I can only speculate this might be the problem.
The extra undead summon is unnecessary when the enemy is dying faster and it isn’t until the end of chapter 4 where defensive harmony becomes important. Lower Dorn’s Deep can be pranced through until you get to the lich but once again, he mostly summons and those mummies can stun your party so attack buffs to take them out fast are still the order of the day (turn undead is a still crap shoot here). The bronze sentries are rather nasty though (especially on insane difficulty) but the multi class cleric still has the buffs required AND the attack power to help pull the party through.
kmonster: Near the end you have level cleric level 17 vs level 12, you can prebuff with 5x magic resistance for 34 MR each instead of 2x24 MR (MR protects from dispel magic and other spells), only the pure class can heal from the distance with resurrection, ...
There are many useful cleric spells you didn't mention and most are more effective at higher casting level, resist fire/cold allows using special tactics, entropy shield offers great protection, ...
There are many other possible tactics than using brute force and a pure class high level casters encourage more flexibility.
That magic resistance spell is useful where exactly? The only place I could think of was the fight with the Kraken Society mages but there were potions available for that. The area in Lower Dorns Deep with the idol is also a contender but you have a lot of room to move there, summons were still better.
I mentioned already using entropy shield over heal is a waste, especially on a character that can’t hit anything on the front lines in the first place. If you want tankage, summons are the way to go and save that slot to heal an unlucky frontliner.
kmonster: It's also more fun having 6 characters with different strengths and weaknesses working together as team than having 6 fighters with little other abilities from second classes trying to steamroll everything.
That is entirely preference, which is fine, but that doesn’t make it more effective. I have cleared with game with a 5 fighter 1 ftr/thf before which obviously, is not the most effective party. The easy areas were very easy, but the hard areas could get really hard. Summons were not a tactical option and damage potions and buff potions had to be used sparingly as there are only a limited amount in the game. I almost ran out of potions of clarity fighting the harpies in TOTLM for instance. Regardless of how you play, the one thing that is constant is to win a war, you have to defeat your opponent and you can’t do that by dragging the war out with unneeded defense and yes, those buffs were talked about earlier are mostly not needed. You should only have enough defense to maintain attack momentum, anything more is wasted energy that could have gone into attacking.