[lost_name]

If memory serves, Nintendo hasn't been very enthusiastic about traditional multiplayer mostly due to negative player interactions (I recall seeing people being autobanned from Smash Bros because of repeatedly attacking the same person). They just want their players to have fun, and I think that it's possible (likely?) that Nintendo wants the ranks to be inflated. I'm sure there's some correlation to the fun factor and improving your own rank, and the server does not need to use that letter grade to make matches.

I think there may be an inflated letter grade for the players to show off, but the server ranks players against each other by another metric that is only loosely tied to that grade.