There are 2v2, 3v3 and 4v4 team match making. They all are pretty similar - automatically created team games. Currently they all have separate rankings.
In TMM more than 90% games are played in 3v3, rougly 8% in 4v4 and less than 2% in 2v2. Thus 2v2 and 4v4 rankings does not represent any value. There are numerous examples of people actively searching all tmm options, getting only 3v3 team games and being unable to calibrate their 2v2/4v4 rankings.
Since it's very rare to find and 2v2 & 4v4 game, those rankings do not represent any value. They are not realistically achievable and are not correct. The mere calibrating to get gold or diamond badge can take up more time searching in queue than in game.
Rankings would be more accurate and less streched out if all TMM games (except 1v1 ladder) had unified ranking. When players have the same ranking in 2v2, 3v3 and 4v4, whichever they find first.