Well he is too strong and the odd ball in the group. There isn’t a matchup for him. Besides knowing Kuzan’s character it’s impossible he turned evil and face the main cast. It’s too suspicious from the start even Burgess noted that out and it’s only a matter of time before he tells BB I told you so. It’s not even entirely about the power of BBPs cuz he either way is bound to be the greatest obstacle to PK throne and the final pirate to face the SHs.
BB pirates are not evil lmao, they are just after a goal, being evil is not a requirement to join. BB wanted Ace to join, he didn't even kill him when he refused, BB simply cares if they are strong or not. Even Oda said he would want to be in BB pirates if he was strong.
BB pirates are no different than Cross Guild. Only that Buggy leads random Impel Down prisoners, BB leads the strongest Impel Down prisoners.