It is all subjective and I think Inoue has as much a valid claim as any, but for me personally it is Usyk.
Inoue fought 4 times in the past year. Recently beat a top 10 P4P fighter. Inoue is the clear P4P number 1 not even debatable.
There are two kinds of pound for pound rankings, career and current. If you want to say that, among active fighters, Oleksandr Usyk is number one for his career I may disagree but I believe you would have a valid point. As far as the last year or the last two years are concerned, it is hard to make a case for Usyk. In the last 20 months all the Ukrainian southpaw has done is defeat two men that he already fought and beat. Naoya Inoue has defended his unified title six times over the same period including his relatively one-sided win last week over a pound for pound top ten fighter. It's hard to argue that the current pound for pound best is The Monster.
How do people continuously get Bivol into this conversation? He lost to a 40 year old with no knees, has never fought outside 175 and is super inactive. He's not in the top 5.
I prefer the heavyweight division, but Inoue's domination of 122lbs blows Usyk out the water. He has been a very active champion, defeated the guys who fans were saying he would struggle with, then put in a great performance at the weekend against a fellow top 10. Usyk is doing the opposite of fighting all comers. Inoue was already #1 for me, this just put more distance between them
I can't see a legit case for Usyk. And that's not a knock on him at all, just that he's not doing what Inoue is doing. His inactivity and rematches are what hurts him.