As most of the fanbase believes, the Straw Hat Pirates and the Blackbeard Pirates will fight for the title of the Pirate King’s crew.
Here’s the “match-ups based on roles” scenario:
I wouldn’t say that matching the end fights based solely off roles facilitates everyone’s optimal match up. There are several scenarios where a more optimal set up of match-ups occur (one of many potential examples outlined below), but these scenarios vary based on which new characters join the Straw Hat Pirates or the Blackbeard Pirates, how the Straw Hat crew progresses, new information we find out about the Blackbeard Pirates, and arbitrarily who Oda decides to match up with who.
It’s impossible in my opinion to speculate exactly which more optimal scenario will play out, so simply aligning by role is my best guess as to how to nail all the final Blackbeard Pirates vs Straw Hat Pirates matchups.