I feel that it isn't clear enough (in the interface, but also the help pages) what counts as Competitive (MatchMaker) and what counts as Casual (Custom) rating ?
For instance it looks like that not only 1vs1 counts for MatchMaker rating, but team vs team (and even coop vs AI/chicken ?!) count too, while AFAIK they don't ?
Rank is the player's level indicated by the shape of the icon.
But rank is also
the player position on the rating ladder !