Blackbeard and Luffy are two sides of the same coin. He's an intelligent, ambitious, opportunist, and a cowardly man. There is a great setup for Oda to portray Teach as possessing overreliance on devil fruits which should in theory lead to his downfall.
CoC means you possess the qualities of a king, right? In my opinion, there are different kind of kings in One Piece. Some are wise, others are brutal, charismatic, tactile, villainous etc. The main theme that ties a lot of Conquerors together is their unyielding spirit in the face of death.. and Blackbeard was ready to throw his dream away long ago if he didn't find the Yami-Yami.
I think in the end, we're looking at a "dark horse". Blackbeard does not follow the usual norms and rules but he did manage to get a bunch of infamous people to stay on his side when they could have just bailed. There is a certain skill in doing that which sets him apart.
Blackbeard has goals far beyond becoming a pirate king and already achieved so much in a short amount of time than what others spent decades working for. Whether or not he needs conquerors haki for his ultimate dream is up to you.
Personally? I don't really care, he's a great character and upsets the status quo. He will turn Nika's smile into a frown.
