I think the parts of Dressrosa that were poorly done were:
the moment Ussop ran way from the trebol/sugar fight when Robin was turned to a toy
the cheap way Ussop won that "fight", which was then used as a plot point later, so that Ussop could develop as a character
obviously block D was poorly done mainly because going into it you knew Rebecca would have to win, but you also knew she wasn't strong enough to do it cause she's a trash character, but we only got glimpses of that so that helped
Sugar waking up a 2nd time was unnecessary except for the fact Ussop needed a true sniping feat and development, but since that chapter Oda hasn't really missed
I didn't like the reset after the string clone got its head cut off and Pica threw everyone out of the palace, it seemed excessive, but it set the stage for the bigger battle.
The 3 chapters of running to the flower field were a little much, but at that point, with so many character converged at once you either take it slow or let some readers get lost. Idk if you visit other forums, but people get lost over simple things in series all the time.
Those are the main ones that come to mind.
I don't mind Sabo vs Fujitora being off-paneled because that's how Oda has been with top tiers the entire series just giving us glimpses of them, while he attempts to save their big moments for when Luffy and co. get to them.
Everybody knew the Sunny group vs Big Mom wouldn't come till after Dressrosa was finished, so why even bring it up as an issue? There's already too many characters to give panel time to on the island, so why cut to ones not there?
Sabo, I'd probably have preferred if he had actually been dead, but we got hints the was alive. It seems for the most part the revolutionaries are good at keeping things quiet like people not knowing Dragon was Garp's son and people thinking Kuma was just a pirate and not a revolutionary.
Luffy always makes stupid moves and underestimates his opponents, just because he has to be slowed down. It's not ideal, but its been part of the series since early on, it's not exclusive to this arc.
I don't think Dressrosa is the perfect arc, but I think overall it's been good. There have definitely been some poorly done moments, but there's definitely been a lot more good and great moments and since about chapter 753 Oda seems to completely regained his form and hasn't really missed. After this flashback we should get fights and then closing up all the dangling loose ends. The arc suffers from trying to be overly ambitious, which in turn has slowed the arc down and caused the most problems.