I agree about lifegems being a horrible addition, they fundamentally change the game's general pacing and bossfights too much, and not in a good way. What kind of crack were they smoking when they added those? I mildly disagree about weapons degrading, but it's such a minor mechanic that i won't bother to elaborate on the point. Weapons pretty much not breaking at all is equally stupid in my opinion (why not just remove the mechanic entirely instead), but it's just an opinion.
Now about the bossfights. I think you have valid arguments here (up to a point), but i'll try to demonstrate that my viewpoint is valid too. It's ok if we disagree :) Ok, so anyway. You don't have to light up The Lost Sinner's room (in fact, i havent done so at all in any of my playthroughs) and it doesnt even make any big impact on the fight, it's mainly a convenience tool. And the fight gets significantly more hectic in NG+ because of 2 additional sorcerers there. Pursuer is a fair and fun earlygame fight even if you dont abuse ballistae, and there's even a one-time option to kill him on the roof before that boss room. I thought that was very cool. They don't force you to cheese him, but you can choose to if you wish. And he's actually entirely skippable and optional! The whole game can be completed without encountering him even once, even though it doesn't feel that way on the first playthrough. Another little example of a quirk that i enjoyed is the first Dragonrider fight, where you can raise an additional platform to make it easier to fight him... which you will most likely do on your first playthrough unknowingly. Or, instead, you can skip this thing and try to make him fall in the water and instadie. And it feels good to "outsmart" him in this fashion. These examples are totally different to Yhorms room, which is absolutely horrible, - kind of like fight with Vendrick, which was megastupid too. You simply have to give in to the gimmick, there's no workaround. But at least Vendrick is an optional boss, and not one of the four main bosses of the game, so the gimmicky fight can be forgiven a bit. I agree about Mytha though, what a lost opportunity there :) There's another example of a failed "timed" fight - in Flexile Sentry room the water level raises higher and higher, making it harder to fight, but the boss dies too fast for you to feel any hindrance. I didn't even know about that until reading about it recently.
All in all, i think Miyazaki could borrow some really good ideas from ds2 bosses and polish them, but he seems to have ignored it completely, which saddened me a little tbh. And while ds2 indeed had laughably bad design in several areas, it had a lot of overall freedom. So i don't see ds3 as a direct improvement in level design, because while it's more thought-out and tight, it almost completely lacks global freedom. As an example - the difference between the All Bosses and the Any% speedruns in ds3 is only 9 minutes. In ds2 the difference is 1.5 hours (with DLCs though, but it was over 30 minutes before dlcs, with varying routes). Still, ds3 is a really great game, which fixes a lot of problems ds2 introduced, but i feel like ds2 doesn't deserve enough praise for its good ideas (and i think it had plenty), but gets more than enough bashing for its downsides. I'll try to avoid delving into the offtopic lands, but will read if you reply of course >:D
Can't choose what to play right now, so back to PoE for a while, even though ultra fed up with it.