Let me preface this by saying you guys are doing good work under the circumstances you are under.
While I did not like the previous iteration of UBC, in a vacuum it was better than this. There was some semblance of thought put into previous UBC and where you had to land to detonate by the player, or running out on a gcd to capitalize on getting it right. I disliked UBC for the fact it was tied to latency, and thus made it unreliable to some.
We got new UBC (Fel mastery) back in its stead but at a lesser value? Can only be used via immolation aura and damage is sub optimal compared to options even uncapped as far as the math works out. But it looks like we got a worse Fel Mastery.
Fel Mastery (150% Fel Rush Damage)
UBC (X% End of Fel Rush Skill Shot, haste effected via Immolation Aura)
UBC (300% Dmg Fel Rush on 30 sec cd, haste effected via Immolation Aura)
You went through all this iteration basically to just gives us Fel Mastery back on a 30 second cool down with haste effecting it via Immolation Aura.
While I don’t mind the idea of the new UBC, it is rather weak by comparison, and I just don’t like the idea of priming Fel Rush with Immolation Aura. Immolation Aura makes us want to stand in the pack, there are things that are built around this-
And via Fel Bombardment
That is 2/8 Legendaries being tied, and 2/4 Potency Conduits being tied to Immolation Aura uptime in some way or another.
While Immolation Aura only has an uptime of 6 seconds, having to delay damage to pull off an empowered Fel Rush does not feel good; as we all know a lot can happen in 6 seconds. Priming with a different ability would be nice, but not something that prolongs us wanting to be in the pack (suggestions would be Eye Beam, Vengeful Retreat, Chaos Nova).
One idea someone mentioned that I liked, have Immolation Aura (for ease of talking about it), change our next Fel Rush to Infernal Strike (obviously damage enhanced version of Vengeance). It’s already apart of the class (not spec) tool kit, easy to use, synergizes class abilities, can be used for interesting mobility or damage.
TLDR; Buff Unbound Chaos damage to compensate with other talents on same row, and find different ability to prime Fel Rush.