Oooo boi, this argument.
Look, lemme put it like this, One Piece's story and cast might be big, but you seem to mistake that for depth. Because, like Toriko, what One Piece has in scale it loses in terms of everything else, namely emotional connectivity and throughline. OP's cast have very little in the way of arcs or depths at this point, it's all large moving pieces.
I'm doing an essay elaborating on this so I won't go into too much depth (might share it here), but I think the simplest explanation for Kimetsu's rise is simply that people cannect to the characters. Tanjiro and his allies have a strong, fleshed and diverse set of personalities with backstories and emotional resonance that each make themselves easy to get attached . It's the same deal with MHA, BC, JJK and plenty of the other series which are popular today, they're all heavily slanted to the characters because that's what readers want.
Like, there is a pretty obvious reason why Jump's current readership make up the minority of One Piece's.