Reposting a good take on this
One Piece is about wild moments, weird powers and creatures and corny shit about friendship and determination. And I think it's pretty funny.
It's never been good at pacing, or subtlety, or nuance, or maturity, or whatever else you expect from stuff that doesn't get labeled "trash". And it's very formulaic. Like another anon said, this stuff gets more noticeable and frequent the more it goes on, but it's always been there.
Point being, even at its best fighting shonen will only ever be cotton candy and it's never "well written", but as for whether it's actually gotten *worse*, I don't think so at all. I actually find Dressrosa easier to binge read than something like Skypiea because at least it feels like things are always moving somehow.
But if you wanna judge it entirely within its genre, there's probably a reason (beyond mere nostalgia) I still read One Piece but can't handle stuff like MHA or AoT or even Naruto. And honestly, I think it's that Oda just embraces how trashy it is. It's always very cartoonish and even the more "serious" moments tend to have some humor or ridiculousness to them.
And I make this point because I think it's easy to scoff at shonenfags who cream their pants over every minutely "hype" moment achieved by violating good taste and common sense, but One Piece seems different because it is very much aware of what it is without descending into outright cynical parody. This is one of the things the first Dragon Ball actually got right, so it's a big plus.
So it's trash, yes, in the best way, which still might not be enough for some people. That's fine.