I blame his post-timeskip editors.
A good editor's job is also to put a stop to the unecessary stuff.
The thing is that One Piece became extremely popular right before the timeskip, and the series was basically too big to fall so they had young & newbie editors that are One Piece fanboys to oversee Oda and were unable to reject any of his ideas.
The biggest problem was one pieces success during ennies Lobby Impel Down and Marineford.
These arcs became the bones of what Oda builds his current arcs in. The whole run piece scene started with Impel Down and Marineford. This also was the origin of Luffy Piece as well as minor characters getting major shine.
The popularity of these arcs made the editors likely think that this is what people want, run piece with lots of big scenes and big character casts. And because of the popularity of ennies Lobby, one piece became a much more battle centric manga where they don’t even explore islands anymore like we saw in arcs prior.
Because of this we have a generic battle Shonen with too many side characters clashing and taking up panel time