Currently the proc doesn't scale with dmg modifiers, but in the tool-tip it does. Lhivera got them to confirm something was wrong.
This is how the tool-tip works.
200% of sp, say we have 40k, 200% is 80k.
It does 80k over 4 seconds.
THEN it adds mastery, so lets say 100% mastery, (on ptr my highest was like 92 with raid buffs...so 100 will be attainable for sure)
100% of 80k is 80k.
THEN rop is the next layer of dmg modifier it takes 15% OF 160K...Not 15% of 80k, 15% of 160k. 184k total, this is without procs or arcane power.
Lets add 2 int procs, total of 30k int more, so that adds 30k sp. That 30k sp goes to square one of the cloak proc.
so 70k sp, 200% of that is 140k.
Then 100% of 140k is 140k more, 280k.
Then 15% of 280k is added on top. 322k.
Then arcane power too, it's during burst lets say, time warp is up and that increases the rppm quite a bit as well, which makes it so your likely to get 1-2 procs with all these buffs up.
So 20% of 322k is added on top. 64.4k more.
So 386.4k during burst, over 4 seconds. It scales exponentially because the damage modifiers don't add the base damage, they modify the current damage. In the tool-tip this is how it works, I did extensive testing on it and the numbers always matched my numbers.
386.4k during burst is pretty strong. Granted that won't be always, and other mage specs will still see the scaling with int and rop/invocation. But without arcanes mastery it won't reach nearly as high. The overall damage won't be too far ahead because frost will stack haste, more procs. Fire stacks crit, the proc will crit more. So the overall dmg for arcane will probably only be 1-2% higher. Not overpowered, and of course the proc scales well with fire and frost. It just scales best with arcane.
Right now the proc is broken, so we have to wait til it's fixed. But this is why it scales exponentially.
If you take just mastery and rop you are still at 184k. And every 1k spellpower added, adds an exponential amount of damage, 1k sp won't just equate to 4k dmg, it'll equate to 4.6, then 1k more won't be 4.6 it'll be higher -- This is why it'll be strong for arcane. Exponential scaling, similar to how fire scales.