Right, it is time to acknowledge this issue. No story lasta forever, no writer can go on for decades. When I think about supporting characters, I have a list:
Oden was a big shot,
He had 10 scabbards
His father's interactions, the Mimawarigumi,
Scabbards have their background stories,
Those background characters have their moments (Kinemon's wife, Yasoi's child, Gyukimaru, and so on).
Then there is Orochi, his 2 forces,
Orochi's past, linking the old hag in his past to previous legends.
And at the end, scabbards did nothing to Kaido, Orochi did nothing to alliance and Kaido.
When strawhats are going to do most of the work, then why hype other characters to the point that it seems useless. Dont forget about that Robin hood kinda guy. A lot of things can be simplified, but no, we have to stretch everything for world building.