One can argue that One Piece won't change much without Zoro around.
But here is the undeniable fact: One Piece is really different if there is no Luffy around. For the better, that's it.
No more spamming "I am Monkey D. Luffy, the man who will become Pirate King" trash like a broken record
No more bullshit like "are you having fun, Kaido?"
No more dragged fight because Luffy with his trash AP can't finish his opponent quick. It is very boring, everyone else even weakass Sanji already completed his fight like 15 chapters ago, and here we go with Luffy's fight, still going back and forth, dragging to no end.
No more sitting duck who kept being saved by gladiators, Zoro, or Franky
No more prophecy devil fruit, as opposed to what had been stated since chapter 1, actually Gomu Gomu is Mythical Zoan cuz why not
If there was no Luffy around, One Piece would have kept its throne as number 1 manga in yearly sales.