Well on mages, you have to consider their specialization if you're playing on nightmare. Also there's a 3rd mage, Dorian, you might not have him yet though but he's imo the best mage character in terms of dialogue and shit. In terms of spec, Dorian and Solas are really good while Vivienne gets the shaft since she becomes knight enchanter, which the AI is fairly terrible at playing. Though you could ignore the spec and make her a decent support mage just with basic skills, basically all the spirit barrier shit and then a few offensive spells like chain lightning+immolate and you'd be alright.
Once Solas unlocks his spec, he becomes insanely good at doing well, his spec stuff, Riftmage is super strong. He is kinda boring though as a character, but he does often have something to point out about the history of places and shit so I don't mind him too much even though he looks like a weirdo. Dorian is a damage powerhouse once he unlocks his spec, though you need to mix it with normal magic for like mana regen and more dmg.
In terms of AI, they use spirit, lightning and fire pretty well, but they're terrible at using most of ice, I think they cancel blizzard instantly sometimes, they don't cast ice wall or ice mines, don't move away from melee mobs with the blink, so mostly it's all about that freeze CC but that's just 1pt you don't really need a full ice mage, unless it's your main character and even then it's kinda meh, icewall blocks vision both ways so it has limited uses and ice mine is clunky. I'd get one for barriers(like Vivienne) with a small dash of every other magic for good damage, one for pure damage potential(Solas or Dorian, with their specs and a dash of other trees for more damage) and spec yourself into damage also. 1pt barrier is fine on everyone, though AI tends to stack it like idiots.
As for 2H, it's pretty alright. Thing to consider about crit rate is it scales with Cunning, so you can craft armor with high cunning and what not which will boost it a decent bit. But those passives are otherwise fairly bad. Good thing is once you unlock specs, Iron Bull don't really need most of the 2H tree stuff, he can use like vanguard/commander trees(I think it's commander, the one with shouts and the pull) mixed with his spec, and ignore 2H entirely. Note the AI is terrible at using whirlwind and pommel strike isn't great unless you're a templar so you can combo off it(but you can do that using another templar ability so it's kinda pointless).