Honestly - the more I think about this, the more I think Plarium is actually probably in the right here. Brimstone really was just absurdly strong, so much so that it made basically everything else secondary. Yeah you can argue that whales will still benefit from it but hey - whales play a different game than the rest of us, so who cares?
As long as they are actively planning on continuing to balance the rest of them, I'm on board with their plan. By far the biggest ones they need to address first are Incinerate, Lethal Dose, and Crushing Rend. The former two because they are almost completely pointless - there's really no world in which the arena meta somehow morphs into one where poison or HP burn are viable strategies, not when there are just so many ways to remove them, and the latter because of the absurdity of it having absolutely no purpose without being at 6-star.
Fortunately, they're both pretty easy to improve. Make Incinerate and Lethal Dose work *everywhere*, and make Crushing Rend work for *all* attacks, and not only the first one.