How comes I have top 400-800 rank on nearly every single ranked/approved top difficulty from last 2 months but my PP says there's over 9000 players better than me? They just don't play the newest ranked maps and just play old maps with high play counts? That's the only explanation I can find.
Your problem is that you are going about it all wrong. That is a terribly inefficient way of going about raising your pp. Two things to keep in mind:
1. The system does not care about scores higher than rank 500. Then again, few people do anyways so it all works out.The system mostly cares about your ranks that would make someone go, "Hey, he doesn't completely suck after all!"
2. Due to how the system works, you need to get a certain amount of really good ranks to get a high pp count. Getting a bunch of 400 to 500 ranks won't really do much.
I recommend SHing some Hards. At your skill level that should be an extremely easy task with some patience. Also,I would improve your top 500 scores that you have that don't have an impressive accuracy (especially the ones that you feel have a lot of weight). Simply improving an older rank's accuracy by a few percentage points can give you a noticeable pp boost.
EDIT: And good thing KRZY admitted to saying that he hadn't tested his theory yet, because nah, it doesn't work that way. Decent theory, but nah.