Luffy already rocking 3 types of adv haki, zoro rocking 2 types of adv haki, while Sanji has 0.
As a CoO specialist he needs to at least have that to adv levels if the monster trio is to be a thing. Otherwise it looks like this:
As a CoO specialist he needs to at least have that to adv levels if the monster trio is to be a thing. Otherwise it looks like this: