Instead of it being cosmetic, have players wearing the C or an A affect the team a little. Various factors will determine the leadership stat, such as age, years spent with team, and past playoff success. Perhaps the small boost from choosing good captains allows prospects to develop better, especially on a rebuilding team. If this implemented, it would be nice to allow the ai to auto pick captains like auto scouting. (It would also be cool to have an option to have 3 A’s instead of a C and 2 A’s)
I made a quick concept image
(Leadership values are random)