Well yes, I agree that everyone has their moments and they all play vital roles, sure, but I believe that Zoro for Luffy is a step above, and there is nothing wrong because it would be like complaining about having a best friend (and therefore elevating a friend over others ), and the problem is this: many fans think that if one is vice-captain, their favorite character is being belittled, so Oda cannot afford to make it official. Obviously Luffy is not the type to say "you are the vice-captain" at most he would say right hand, let's remember that Luffy is the same one who thinks that alliance = friendship, because he interprets things in his own way. But I think that if Zoro has often held the role of vice-captain and he is considered as such by both the characters and the databooks, there must be a reason, don't you think too?
Urouge and Bartolomeo are external to the crew and yet they say that Zoro is the vice-captain, in my opinion it is not something not to be counted, because behind their words there is Oda. and why would Oda delude fans with something that isn't true? Also, Bartolomeo is a fan of all straw hats, he is especially a Luffy fan, but he only hinted Zoro at the role of vice-captain.