Monks and paladins both do fine. There is more than enough damage from a lot of classes in this game. "Can kill any boss in two turns, alone", enough damage. I don't know how ranger does, nor a pure Wizard. The numbers don't really matter when everything just dies in two turns
Wizard does fine with the Ramazith tower scrolls and clown gloves. Warlock with magic missiles works and has an EB build that's decent.
It's druid, ranger, and bard that are in the gutter doing less than half the damage. Cleric too, but that's understandable because cleric buffs are super busted and neither druid or bard compete with cleric buffs, so they're just gimped clerics.
The problem is not the Fighter but the insane gadget and item policy of Larian, coupled with some action design decisions (like Haste). Fighter would be problematic in aoe tasks for example, if there weren't the ridiculous magical arrows all around.
I wonder however why the "casters are sooo bad" whiners hint to the many unfair advantages for melees but forget that lots of mobs are resistant to all physical damage, and the effects of Wet. Partial bias, maybe.

Because enemies are also resistant to magic, and missing a lv6 spell/doing half the damage on a save or getting counterspelled feels so much worse than a martial class who just gets to autoattack again the next turn.