You thought that bad class assignment only happened on BG, but apparently not.
I am playing Alley of Blood and I keep getting matchup like this: 3 Tanks+1 DPS VS 4 DPS in the game mode where you need to destroy the tower to reach the core. Guess the outcome? The team with 3 tanks easily wins those games as they can easily push and destroy the tower with their insane mitigation and immunity while 4 DPS just watches at the sideline or die trying.
This is a game mode where everyone’s stat got equalized so it is really beyond me why don’t the matchmaking assign the class evenly or closely like 2 Tanks + 2 DPS VS 1 Tanks + 3 DPS instead of 3 Tanks + 1 DPS VS 4 DPS.