I guess one of the primary reasons why Zoro fans dislike Wano is because Zoro, someway somehow, is both significant and insignificant at the same time.
It feels like he is involved in many plot-lines, yet they don't really go anywhere.
A few examples:
- Zoro bonded with Yasu and promised to avenge him, yet nothing relating to this has happened so far.
- What is the purpose of his relationship with Hiyori? Is it simply so that she can give him Enma?
- Zoro's interest in forging a black blade got brought up twice in Act II but nothing.
- Zoro looks exactly like Ryuma and Ushimaru, why does this matter?
Another funny one.
In 997, Zoro says that he came to Onigashima specifically to slay Kaido. Of course, this so far has gone nowhere, and it ends up being that his main goal of the raid has been abandoned so that he can fix a problem (no one fighting King) that didn't need to be there in the first place. He isn't the only one who has had their arc goal be dropped, the same happened to Kid.
Why? So that Luffy can shine. The problem isn't that Luffy is getting to fight Kaido all alone. It's that Oda bothered to create these 'goals' so that characters other than Luffy aim to fight Kaido, but in the end they got moved around to fight characters they didn't care at all about.
If Zoro's end purpose was to defeat King, don't make him have a declaration saying he came to Onigashima to fight Kaido.
If Kid's end purpose was to help defeat Big Mom, don't make his entire arc mission to defeat Kaido... Lol
A future potential problem that I see is Zoro's acquisition of Conqueror's Haki not being important besides as a power up.
Again, it feels like everything is set up for him to have a leadership moment tying everything starting from what he said in Zou, but it still feels like Oda might simply not care.
If the ending of this arc is anything like Thriller Bark, which ended with Zoro's biggest character moment in the story, even until now. Then, many of the problems can be 'solved'. Maybe the Grim Reaper is the start of this moment, who knows? But if nothing happens (no pun intended), then it really seems like Oda came up with a bunch of ideas for Zoro, then gave up mid way.