Personally, I think FD4 is fine as its own button, as it helps compartmentalize between the setup and push-all-the-buttons-now! parts of the burst. It also leaves space for future updates to maybe add more chances to use FD4 outside of Flourish.

Starfall though, could really just change the Devilment button. If not outright replace the ability itself so it grants the buff and does the damage in the same press. Being that Starfall auto direct crits, it shouldn't matter if the buff portion somehow lags and doesn't apply before the damage?