Crowd control because after that, your only goal is to survive until you can cast again.
Tank because if crowd control fails, your mages die with 2 hits in the early game
The AI CAN NOT counter a first-strike that happens "out" of combat.
But with infinite mana + cooldowns, there is no reason to hold back. You should ALWAYS cast your biggest spells first, because the cool-down starts earlier
Crowd Control/Tanking. In general in this game you try to crowd control above all else, once you have that you have the win. Tanking isn't even needed, only needed if you can't get control, which can be rare as you mention.
The part of First Strike Out of Combat, really that is a player exploiting (beyond scoundrels). Being single player no big, but if anyone knocks combat because of taking advantage of this, they control that and can look in the mirror. Perhaps Larian should look at something to stop that from happening.
In my re-balancing what I ended up doing was up cooldown turns on damage skills for the magic lines. Lower AP cost on many buff/debuffs, because as you mention the tendency was too strong to go with damage almost always, damage with CC even more so. Now when I have 3 AP left over I have some buff/debuffs to consider.
Other things, lowered CC hold rounds, pretty much took off one full turn on every hold in game, both sides. Lower the chance to land a CC status affect, another thing that was too strong. Adding points to INT nicely adds to a higher chance to land CC's, but the general starting point imo was way too high.
I'm not a fan of Int being tied to cooldown, when you concentrate heavy on Int for a Mage you can easily go over 20 points and way too many magic skills can then be used turn after turn. You can't do this with Warrior/Ranger/Rouge skills they are always static in cooldown. But having mage skills always available each turn is a pretty bad thing for strategy. I'd unlink cooldown to INT and make it so all cooldowns are static, the damage boost and % to land CC increase is well enough bonus to make INT worthwhile.
Rebalancing in those manners makes you use other non-damage skills more often and to me makes it a better game.
I also knocked 5 points of Initiative right off the bat, the game is much more interesting when your team doesn't go first all the time.
As you mention with infinite refreshing skills (which I like), this is powerful and makes your guys very very resilient in nearly any battle. Having the enemies have a chance at going first or mixing both sides through the chain, can make some fights starting your side out in a good hole, but a hole you can climb out of due to the system. These scenarios have made the best moments in the game for me.
Another thing I've been tossing around is limiting how many skills schools you can build up. Every skill you should be able to put 1 point into it, but have only 3 skills in which you take higher than 1. What I've noticed is casters for example you can have nearly everything and every caster has the same skills. (Pretty much any group in which you have the same class of character within it) It would probably be better strategy if casters were more specialized in only a couple/few schools vs them all. I think there is something there to improve on, maybe a future game using same engine.