Magic is poorly designed in DOS2. Nobody will deny that.
Magic is just not worth it.
Was there actually once a time, where you had to say something nice about Divinity Original Sin 2. Because since i'm here and saw your Posts, there was only negativity and hatred. Maybe i simply hit the wrong posts, could be possible as well.
And no, i won't deny it, because denying would imply that your "Opinion" is an "Fact", which someone don't want to accept. However your Opinion is simply only that; your Opinion.
Magic in Divinity Original Sin (plus 2) is actually one of my Main-Appeals of the Game(so the quite opposite opinion which you try to force on us). I love to play Magic-Builds, and not only Geo&Pyro-Kombo. My actual Main is an Paladin-Style so Fighter Combined with Hydrosoph plus Aeorothurg, and he is so fun to play. For one you can Heal, for other you can Freeze, also Blind and Stun. You blame Fire for make most Damage, but Aero and Hydro focus on CC. News for you, most Proper RPGs handle it like that. If all of this would be focused on simply make it Damage, than there wouldn't be any need for Elemental(-Diversity) at all. And if you imply it doesn't make damage at all, than you clearly do something wrong...
And that Rogue's are so strong, tells more about Rogue then about Mages, because if i consider one class as way to overpowered, its Rogue...