You aren't understanding, in 3v3, you are only focusing on 3 players (when joining as random), therefore it is easier to negate a new players 0.1kdr (who is on your team). However, in clash or control, you have to worry about 6 potential players, and if you join as a random, it's luck of the draw for how many 0.5kdr players, and lower, will end up on your team or the other. Either way, if you join as a team in either match up, at least coordination is present.