I just had a couple of games, with a premade 2-2-2 and my observation was, if the DPS is bad, the whole team loses. You can be the best tank or healer in the WORLD - IF THE DPS IS BAD YOU LOSE.
I think blizzard doesnt know themselves what to do. They wanted a team game, but nobody wants to play healer let alone Tank. Many times in premade groups of 2-2-2 - THE TANK ROLE IS THE LAST TO BE FILLED! Especially shield tank rein or orisa nobody wants to play - and my observation is most of the time - the team with no shield tank loses. How many times you see a 5 stack of DPS waiting for you in quickplay when you join the previous person having left.