Arcane being such heavy before the nerf was ok in my eyes.
Arcane needs much more Mana and in long fights 5Min+ it won't be such strong. The nerf will make it weaker and more difficult to play. If now Fire will be stronger over 5min+ fights it will be very boring in ulduar.
I hope there will be another tuning that arcane is also on the same lvl on long fights. I hope blizzard will tune the different builds in dps like the difficulty in playing them.