1 Shorter cast time for nukes = greater dps
2 Shorter cast time for dots = no dps gain
3 Increased dot damage due to ss = greater dps

1 = 3

So that is the status of that.

Yes fester (and other cooldown nukes, like enkindle) are not affected by SS. But our basic rotation, from GCD to GCD, DoTs and non DoTs, now scales together with each other and that makes models actually more accurate, as you don't have to account for GCD. Simply take the baseline 2.5 gcd, then scale the damage from both DoTs and ruin together.