I have a general question about the class balance.
It feels like Mages are by far the best class in this game,
No. All classes are very viable and offer different possibilities. Rangers lend themselves near perfect for high perception, opening fights with battlefield setting and crowd control arrows.
And one of the abilities of melee I nearly never see discussed are the man in arms skilss dealing resistance and body building/willpower debuffs (lower and nullify resistances, divine light). Powerful tools best applied in the middle of enemy groups.
In short - I always had the best time with mixed groups enclosing all 3 principle types (ranger, mage, melee). Only the 4th class, the rogue (which is NOT a warrior), escapes me - too much patience and caution required to get them going, especially early on. But others report him to be equally powerful.
There is no such thing as a ranking of character "classes", there is only different battleplay styles and different approaches. Not to forget powerful hybrids like battlemages, which I personally regard as useful as a specialized build. Larian has done a good job on class balance.
Regards,
Thorsten