The problem is, that kinda goes out the window when
A) we only assume we know Orochi's powers (i.e. 8 head limit)
B) as a result of A, can't actually be sure he's dead
There's always a counterargument to these kind of things.
What wouldn't have a counterargument is everyone seeing Zoro actually getting up again and claiming he has something else to do. That's my point