Kaido saw King as strong mofo and name him VC so idk where this "doesn't need to be 2 ND strongest " comes from
I don't think SHs are traditional pirate crew.
They all are like close friends and family - Luffy hardly gets treatment of a captain but more of closest friend.
It doesn't need to be official because it brings rank within the crew where bonding is more like friends.
But that doesn't mean one has to twist the narrative to say sanji will be VC or usopp.
It has to be zoro if SHs ever got VC.
There are many evidences projecting so
1) Strength is symbolic to being Captain so this should be applied to being VC as well.
2) Zoro is second strongest and fights second strongest who also happens to be VC of their crews
3)Zoro is considered as VC by Barto in Dressrosa. Thats Oda implying unofficially Op world views Zoro as VC
4) Few characters questioned why zoro isn't the captain.
If people still argue otherwise then they are just being in denial phase