i view it as feature creeping
at first it's like, a huge deal for the ultras to exist. like the first arc would have like one
and then how do you keep the tension up? you keep introducing more and more and more to the point where the super rare is now super common
imagine bleach or one piece or naruto, in that over time the end is just an entirely different sort of story that was first presented, with a cast that just grew exponentially because it had to top the last time a crew of people showed up. it's comical how much it goes from vibes and struggle and triumph, to just these comedically large threats
the original last arc of bleach, the aizen stuff, the almost end of the last arc just introduced like 30 new people, and what did the final final last arc do? introduce a billion more people