To me the biggest difference that makes people feel a lack of tension in the Post-TS compared to the Pre-TS is the fact that Oda started using side characters instead of Straw Hats as the emotional anchors of the arcs.
We actually cared about Sanji in Baratie, Nami in Arlong Park, Chopper's backstory in Drum Island, Vivi in Alabasta, Robin and Usopp in Water 7 / Enies Lobby, Brook in Thriller Bark, Straw Hats in Sabaody.
That's why some earlier arcs like Skypiea / Syrup Village didn't hit as hard for some people, because in Skypiea there's no single important character we need to care about, we have to care about the entire nation and factions, so it's more complex and hard to latch on and in Syrup Village we had to care more about the town and Kaya than Usopp to actually feel tension for that.
I feel like every arc in the Post-TS feel more like Syrup Village / Skypia, Oda creates a bunch of characters part of a nation and wants us to care about them, so we feel tension fighting to save them. But because they are a bunch of characters that end up dividing people's attention and steals the screen time of the straw hats we love, we end up not caring for the islands like we did back then.
Because of that, people actually end up pissed off at those characters we are suposed to latch on and care about the arc, like the Scabbards, Momo and Tama in Wano.