I think the biggest thing about rapid brutality is that it only triggers on basic attacks, so only basic attack killers will benefit. However, basic attack heavy killers are very vulernable to not having bloodlust - killers like pig and wraith could be very hard to play on certain maps without it. Thus, I don't think rapid brutality is as amazing as its made out to be.
With regards to 4.4 killers, who would use it? It doesn't trigger on hatchets, and for spirit, catching up to survivors isn't really super impactful as you have power. Maybe hag, but once again, as hag you're focused on trapping and primarily rely on traps to get hits rather than longer chases.
I think rapid brutality is really strong on paper, but when you asked the question of who specifically wants to use it there are only a couple candidates who would use it well.