Right now I think this subspec suffers from two major things: (1) Proc overload/overcapping, and (2) comparably bad damage. Some ideas to help on this front:
As long as Frostfire Empowerment stacks twice, it feels like Excess Frost/Fire should also stack twice (while keeping the haste/mastery component capped as-is). There are too many times you’re in a situation where you can’t use empowered FFB without overriding/wasting the existing Excess stacks. Being inundated with this many procs leads to some bizarre gameplay where you’re struggling to send everything at the expense of wayy overcapping on SKB. To that end:
Let SKB stack up to 20. This should at least give some room to breathe with respect to wasting stacks. An SKB into an SKB should add to the timer in the same way that Combust into SKB adds to the timer, should the situation call for it.
On the damage front, I think using either Excess Frost or Fire should increase the ST damage of the next empowered FFB. Or, alternatively, using Excess Fire can increasingly amp up Pyro damage, and Frost can amp up FFB (and splash) damage…or something. As it stands, you’re prioritizing Excess Frost PF for the free Ice Nova, and really just using Excess Fire for the PF CDR. Feels like it’d be cool if this priority system were dynamic based on ST or AOE, e.g. getting Excess Fire out first is more important on bosses, while getting Excess Frost out is more important for splash.
I dunno, this just needs some work; as it stands, the way it plays is antithetical to everything you’re supposed to know about Fire (pooling before Combust, chasing/prioritizing Combust CDR/SKB stacks, etc.)