All specs - Make alter time non-dispellable. It’s already counterable via stun. This brings it on par with dispersion / greater fade / etc. Increase cool down duration if necessary.
Make Ice Block non-mass dispellable. Sitting in a block, not being able to do anything should not be counterable. Make shattering throw and mass dispel not work on block.
Fire - Buff fire bolts and leave tier set alone in PvP. No reason to change this from PvE.
Also, make scorch not completely useless. It does zero damage.
Frost - Make cone of cold do something. It’s a waste of a global cooldown. Either buff slows of frost across the board (75%) or add a disorient to cone of cold to help with sheeping.
Everything else on frost is working good atm.
Arcane - This needs the most work obviously.
Increase damage across the board by about 5-10%.
Remove the channeling on arcane missles and make it like flurry where you get instant procs.
Add a stun (baseline) for four seconds with a short cool down. This will help arcane mages sheep / secure kills.
You’re welcome Blizzard! (lol j/k <3)