My biggest problem with arena after a few matches is actually that damage is insanely overtuned. Just comparing the fortify/frost armor spells to damage is eye-opening enough.
1 AP to apply 100 magic armor. 1 AP to cast hail strike and remove all of it, do an additional 200 damage and also freeze the target. With the new system of how CC is applied, the frost armor/fortify spells need to be more effective. Especially with how high damage is, armor just gets stripped away instantly.
It all really comes down to damage for me, which I know will change a lot before official release so I didn't rant about it in the OP - but it's so high right now that arena doesn't feel fun to play. The winner is whoever has a better starting position
which brings me to a valid suggestion
*You should be able to select which position your units start in. When my warrior is on high ground and my mage is on low ground, while my opponents warrior is on low ground and mage is in high ground, that makes me sad.