After thinking about it, so many plot-points had a massively disappointing resolution or no resolution at all this arc.
1) Toki. Need to say more?
2) Orochi's end. After all the talk (Hiyori: "I want to kill Orochi!", Zoro: "I will get Orochi!" etc.) Denjiro of all people cut him down in a manner that 90% of the OP fandom still thought he had to be alive bc it felt so anticlimatic.
3) Kaido's and BM's end. Really no further explanation needed.
4) Zoro's entire plot about avenging Yasuie - forgotten.
5) Zunesha arriving. This has to be the biggest trolljob I've seen in a while. Massively hyped entrance and now it leaves again without doing jackshit or serving any purpose.
6) Onigashima being a "special isle" (Marco) and "there being a specific reason why I'm staying in Wano" (according to Kaido) - forgotten plot points
I could go on with several more.
PS: Out of all the villains the CP-0 guys did by far the best job, actually killing a former YC (Izou) and almost getting Luffy killed if not for plot armor. That's quite telling and not in a very good way ...