Also, while certain items may work better for other classes, it's really only the Fighter (and the Tinker, now - Funny that people like the Tinker) that can make use of pretty much anything you find in a dungeon
The fighter, moreso than any class, is a tabula rasa. It's less that he "works better" with any approach, and more that he has no natural approach of his own and what you can do with him is really defined by what glyphs and items you find.
The Tinker is a gambler class that really depends on what's for sale in the shops. If he were introduced prior to the 50-gold bank preparation or the elite-items shop preparation I'd be dismissing him right now. Definitely one of the last classes you'd want to play purist with, but pretty solid with a bunch of preps to make use of his alchemy toolkit.
A good Fighter player should never be disappointed in a dungeon run, they're playing the king of generalists, after all.
I disagree strongly with this sentiments. Very few classes in this game have crippling specialization (rogue, berserker, monk, and maybe
wizard) which means virtually anyone
should be able to make due on lower difficulty dungeons with a bad run of shops and glyphs. I feel like you're just setting the bar lower for the fighter.
Rogues can't use Health potions if they don't have enough health
Worse than that; health potions are based on max health, so rogues actually get almost no benefit from drinking health potions. If you want to do healing as a rogue, you need to use HALPMEH (which actually works very well
for dwarf rogues). The rogue is one of a handful of cripplingly over-specialized classes. On any reasonably difficult level, it's CYDSTEPP or bust.
Also you don't have enough money to buy everything in a dungeon and finding something like Soul Orb on a dungeon with no mana burners will still make Fighter unhappy (although it makes everyone else unhappy too if not for conversion)
Actually Soul Orb is pretty nice for conversion points. 65 conversion for 15 gold? It's basically the next best thing after bloody sigil and troll heart.
I think as thief as the baseline, because it is okay at everything, but great at nothing.
Quite to the contrary, the thief is great at just about any approach if you've got the right race for it. With more bonuses in play, he ends up being stronger overall than most other classes and he can leverage health potions to supplement his mana or his mana potions to supplement his health even if he cannot use both kinds. While the thief is naturally inclined as a hybrid, it's entirely possible to play him as a pure brawler or pure caster.