Originally Posted by
Nythiz
But this is not the tradeoff.
You're not tradeing a starsurge for a starfall, because the starfall costs 0 AP
What you trade is a GCD for a starfall; which at the end of a fight generally means that you trade a non-empowered solar wrath for it.
That GCD gives you: 9 * 44% SP (starfall itself) + 0.20 * 450% SP (20% chance on a free starsurge) + 192.5% SP from stellar empowerment benefit** = 678.5% SP
**Stellar empowerment is completely gear dependent so I have no clue whatsoever how much it is, but for ease's sake I assumed you get 1/4th of a full MF/SF worth of damage out of it. It's probably even way higher considering haste and mastery levels above 50%. But just to put a number on it i went with 25% of both DoTs.
And you get that for only the cost of a GCD, which would otherwise likely have been spent on a Wrath cast for 200% Spellpower.
In fact I think the stellar empowerment is quite a big factor, which makes starfall pretty competetive to starsurge even ignoring the legendary proc. Given the fact it's completely free should make it a no-brainer use if you can land the full duration.
Disclaimer: Math might be off on some points, but it's more to make a point that Starfall is quite good.