Oda has already firmly established Akainu as a powerhouse though, the only thing left to do is follow up on Akainu’s already magnificent portrayal since the pre-ts. Besides, there won’t be much catharsis if he gets sidelined and treated as an afterthought plaything by Nika. He arguably looked much better than everyone else in MF when WB himself was present there lol. It will be dumb writing and contradicts the power hierarchy embedded within the story if Akainu gets trashed so easily.
Also, characters like BM and Kiz don’t need much focus anymore. They are replaceable because there are other characters that can fill their role like I said before. Kaido, and Teach have been chosen as the main obstacles for Luffy in the yonko/pirates faction. Akainu fills that role in the marine faction, and he also has a personal sin against Luffy. There are only 2 characters in the story in which Luffy holds a grudge against - Teach and Akainu.