I never really understood the Kuzan is a double agent idea. Blackbeards too low on the Yonko totem pole in the eyes of the WG, why send an ex admiral to a 2.2 billion bounty but send Drake to the World's Strongest Creature? I don't think it makes sense.
I think Kuzans character arc where he slowly loses faith in the WG makes sense from what we've seen. Inevitably it moving to the extent of him standing with Blackbeard in order to find out the secret that got his friend Jaguar D. Saul killed would be a great end to it.