4% for 20% haste is super unreliable and kind of overkill. I would much rather have a more consistent, lower amount than some sort of streaky nonsense.
Maybe for other specs. 20% haste during AP is strong. 4% haste during conserve or AP makes no difference 4% haste is like 20-30k dps so.... 1% overall increase? :d But yeah RNG set is no fun.
I like arcane because it's not a slot machine like frost with procs and shit, or at least it's less of one. Having to pray I land on a 4% roll during AP is worse than hoping for a 20% roll.
We know fire set wont go live like this so getting excited is pointless. Best you can hope for is it doesnt get completely gutted like the shoulders were.