@Alfiere:
Sadly, that's been the case for a decade at least now.
Exactly, or as DoctorPhil said the Strawhats' victories don't feel earned.
Starting with Dressrosa, where we actually go for the big shot with 30-40+ volumes build-up, the villains are just lacking way too much - both as a villain group as well as considering the leading figures.
Like Dressrosa, we're teased by Aokiji and Brandnew just how different Doflamingo is compared to everything else. Specifically it's shoved into our throats that Doflamingo has this special devilish charisma. Therefore we as readers ask the powerful question: How on earth are the Strawhats supposed to deal with these Donquixote Pirates - and especially with this super-charismatic and super-popular Doflamingo who unlike basically everything before (seemingly) doesn't have to hide his true colours in front of the outside?
But nevermind, in fact that charisma stuff all is fake, instead everyone and everyone's mother just blatantly hates this guy. All the Strawhats have to do is to turn off that fucking Sr mind-control-device - resulting in Doflamingo losing all his sting almost instantly. Instead of the aforementioned high tension dramatic situation, we get the way-less-tension-riddled question as how to deal with his last desperation moves. Also his crew itsn't anything special. They have decent power levels, but that's it. I don't really care for power levels right now. Besides, Oda's writing completelys fell flat regarding to writing intelligent villains. Any decently (that is, NOT genius or even Aizen-insanely-planning) intelligent person tries to have as less uncertainty factors as possible. However, the whole colliseum scheme is the exact opposite as it invited hundreds of unknown random factors (like a DF user who's just the natural enemy of Sr). Doflamingo is just a generic moron, no matter how you turn it.
Okay, Big Mom. Well, she has the mental state of a five-year-old. That's fine and actually fun and intriguing. But apparently she also had to become a mindless beast without any conscience because… lazy writing. Again, she and her organisation initially were depicted as something special with her mafia-like blackmailing abilities. So the interesting high-tension-inducing dramatic question was: How will the Strawhats deal with this enemy who has the power to (seemingly) effortlessly threat everybody on the East Blue/whole world casually as collateral damage? But again, this point again got dropped for the pure convenience of lazy writing. Same with the Sanji handcuff subplot. Also, the Big Mom Pirates ended up as an extremely dysfunctional group, so we end up with the way less satysfying dramatic question how to deal with these strong but totally dysfunctional enemy group. Which is nothing compared to the original dramatic question which just got shafted completely away just because it's easier to write answering the latter weaker question instead. Also the whole assassination scheme was completely provided by supporting characters, therefore diminishing the Strawhats' earnings even more.
Sadly, the post-timeskip overall writing quality just is plain mediocre. Wano isn't any better as well. Pre-timeskip of course isn't flawless, but this shouldn't excuse the current writing quality in any way. With the recent Tama issue being one of several dozens other subpar writing decision summing up.