In chapter 737 we found out that Blackbeard is supported by 10 Giant Captians, Burgees is one of them. I looked through the other members of the blackbeard pirates.
So the other Giant Captains are Laffite,Van Augur, DocQ, Shilliew, Catarina Devon, Basco Shot, Avalo Pizzaro and Sanjuan Wolf. Including Burgees there are 9 of them, so who could be the 10th Giant Captain?
If Stronger is not just a mount for DocQ i guess the question is answered but so far I think he is just a mount for Doc Q so maybe not.
The person who I think is the 10th Giant Captain so far is Aokiji. In the series Burgees is talking to Blackbeard via Den Den Mushi and they talked about Aokiji. If that is the case then the Blackbeard pirates are really powerful since they got a former Marine Admiral.
I could really think of the other people who could possibly be a member of the blackbeard pirates, maybe a supernova, I don't know so who do you think is the 10th Giant Captian of Blackbeard Pirates?