Even so, she still hampers with my rotation far more than I'd like, so either Blackcat is a lot better than she says she is (don't doubt it) or whatever.

While hashing the idea out in my static discord, another friend who happens to play Black Mage a bit suggested the following change, so Firestarter AS IS would remain, but it would improve the MP economy of Black Mage.

Trait: Astral Conversion: Casting a Fire Spell under the effect of an Umbral Heart converts the Umbral Heart to an Astral Heart. Astral Hearts decrease the cast time and cost of Fire by half and only consume one Astral Heart per cast. If a Fire cast under the effect of an Astral Heart procs Firestarter, the Firestarter will upgrade to Blazestarter/Infernostarter.

Blazestarter/Infernostarter: Your next cast of Flare will have no cast timer and no MP cost.