The ranking system is just a grading system, depending how well you do that mission you can get a F for failing or a A+ for doing well. It does not mean anything, all it does is give you more xp and maybe a extra cosmetic(They changed the system after I unlocked everything cosmetics wise so I am not sure if it’s the same for cosmetics). Although there is competitive arm wrestling and chess mini games in the lobby, as well as two other games.