Actually, from what I can remember from the speedrun, if a dungeon doesn't have a boss, a later dungeon will have a boss, and when you defeat that boss, *then* you will get the stats you missed from all the dungeons since the last boss, so I believe you can't miss stats that way.

I like to have the choice to level up when I want and distribute the skill points (if any) myself. There are games I may not even want to level up anymore after some point.

Semi-automatic, so I can think about my upgrade choices for a bit without interrupting what I'm already doing.

The problem with that is that it often leads to pointless grinding of stupid tasks, such as forging 2000 useless daggers in order to maximize your blacksmithing skill. Or if you have weapon class skills and you've been using various swords from the start of the game, but then you find an awesome axe with much better stats than your current sword. Then you have to go back and kill a bazillion low-level creatures with it because you can't actually hit any creatures of your current level until you have gotten your axe skill up.

I don't have strong feelings one way or the other. All I know is that I detest morrowind and oblivion's leveling system.
If I had to choose, I'm leaning more towards automatic leveling.

Semi-Automatic. Tally stat natural gains automatically, allow further action for bonus allocation/skill levels.

In my case, not like Diablo, but more like Avernum/Exile. You get a small notification, stat gains and then you can go and train up your skills back in town for a fee. (Gold and skill points.)

This.

I am unsure what the system is in e.g. Fallout Tactics. Once in a while one my party members may get that "LEVEL" box on the screen. When I click on it or go to the Character screen, it lets me add more skill points to different skills, and if it a a level up where I get extra perks, I can (=have to) choose one from the list as well.

So in a way it lets me delay making those selections, but I am unsure if the other things related to level up trigger instantly, e.g. does my character get extra HP only when I click on that LEVEL box, or do they gain it already when that box appears?

Anyway, it is an ok system. The only thing i don't like is how slow it is to get new perks, every third level up. I still want that and that and that and that, and I am already only few missions away from finishing the whole game! I wish it would let me pick new perks either every second level up, or even every level up. Maybe every second would be at the sweet spot.

Now it makes me make selections that I don't want to make, like "do I want my character to avoid shots better, or have more HP, or be able to shoot at enemies at greater distances?". I need them all, damn it!

And before someone says that's the whole point, you have to decide what character you make (not have all interesting perks in one character)... when it comes to skills, there I don't normally have to make such selections because by this time I have already accumulated so many skill points to distribute over many skills. So already now all my party members are both first class snipers (small arms skill), as well as using energy weapons, and many are also very good wth big guns. And they all also have very good sneak ability etc., so as far as combat goes, they are already all "jack of all trades". Heck they all are even good at finding and disarming traps, even though usually I end up just shooting the land mines as it is faster (many mines blow up at the same time) and is fun.

Morrowind is manual levelling and not semi-automatic, as you still need to spread the points yourself. There is no difference between oblivion and morrowind regarding levelling, except that in morrowind you need to sleep to go to the next level.
As for myself i prefer the manual levelling as in Morrowind or in The Dark Eye: Drakensang (many stats here to sink your teeth in). Not a fan of automatic. Unfortunately Dragon's Dogma: Dark Arisen is fully automatic. You have no single control regarding your stats. Game itself is nice to play, but i don't like the automatic levelling. That game is also known as Illusion of Time. Played it myself on the SNES and still have it. Game from then Enix, when they were still a seperate company (before they later merged with squaresoft to form squareenix)
Nice game though. But indeed, if you miss something you're screwed. Especially if you plan to get all the 50 gems to unlock the secret level.

A more modern example of what is going on in Illusion of Time/Gaia, is the skill system in Styx. You can equip the character with various skills, each of which require an amount of SP to unlock. However, you only get SP from completing objectives - but only once. The emphasis becomes the completion of various goals within each mission. You can also replay missions to complete goals that you have missed.

I really recommend the Styx games - they are very much like the classic Thief games, but correctly consolized.

I would argue that having to use the axe against weaker creatures to become good at it is better than not being able to use the axe at all because you have spent some of your limited number of points on swords and can't fit axes into your build.

Also, this problem can be mitigated by not making accuracy too dependent on skills. For example, in the SaGa 3 remake, at one point you get a great sword and then have to fight a rather difficult boss that regenerates HP but is weak against that sword. Fortunately, the game is designed so that you have decent accuracy even without good agility or skill (you will still miss, but not all the time unlike SaGa 2), and the first learnable technique of a weapon is easy to learn provided you are in the correct race (in this case, cyborg, and note that race is changeable in this game).

Another thing that would help is having other party members who are still using weapons they're good at. For example, in the SaGa 3 remake, you could just have a character attack with a new weapon type, while other characters keep that character alive. (Also, unlike some games, you get your stat gains and skill levels immediately, so a character doesn't need to survive the battle to get stats and skills, and prolonging a battle leads to more stat growth than ending the battle quickly.)

For your forging 2000 daggers, in a well designed system, you would get more skill experience for performing harder tasks, like forging swords, battle axes, or spiked flails.

Actually:

Oblivion requires you to sleep to gain the next level as well; the difference is that, in Morrowind, characters without Stunted Magicka will be sleeping to recover Magicka (making the leveling semi-automatic by my definition), while in Oblivion there's no real reason to rest other than leveling up (hence making the leveling manual) or getting vampire dreams.

Also, one other difference: In Morrowind, a skill increase after qualifying for a level up counts toward stat gain for your current level, while in Oblivion it counts toward your *next* level. (Incidentally, the way stat growth works is the one thing I dislike about the Morrowind/Oblivion system; if you just got stat points to distribute at level up (like in Daggerfall, but without the random factor) it wouldn't be so bad.)