I've played about halfway through Cyseal with a double lone wolf mage/ranger + mage/rogue, to test a concept build. It was fine. Fairly challenging, given that I was fighting fucking skeletons, and relying mostly on piercing damage, but it actually worked okay.
I cannot even comprehend trying to do that without having invested points in magic.

It's not that I think Warriors are worth less than Rangers or Rogues. It's that I think Mages are worth more than any of them. Essentially it boils down to the fact that I think Intelligence is overused.
Intelligence improves damage & cc chance, and reduces the cooldown, on more than half the abilities in the game.
A character with no intelligence is very limited, compared to a character with (at least some) intelligence. The more intelligence you have, the more effective you become with most abilities in the game.

How does that compare with Dexterity and Strength?
Strength only improves 1/8th the abilities in the game.
Dex only improves 1/4th.
Neither reduce cooldown.
Forgive me if I'm wrong here, but I don't notice that either increases damage, either. If they do, they don't seem to increase it much.

I suggested, at one point, that Geomancy scale off of Strength and Aerothurge scale off of Dex. This would increase the value of those stats - giving pure Str characters and pure Dex characters more flexibility (and synergy), while making it hard to be a master of all elements for any character.
Int would improve 3/8 the abilities in the game, as would Dex, and Str would improve the other 2/8.

I know a lot of people don't like that idea, for reasons of lore, but I think it would improve the balance of the game and essentially fix any problems I have with mages.