If you remove 1v1v1 and make it 1v1, you'd remove any "collusion" or "unfair treatment" but then you'd get one-sided stomps instead.

Look at RW, when you get crushed in the very first engagement, you're done, there is no comeback, there is no other team to help you beat the opponent team, you just lose. 1v1v1 is to balance it out a bit so you have the option to team-up and go after a stronger team, otherwise you'd just get continuous one-way stomps, especially if one side has a strong premade in every match. I think having 100% of your games stomped by a premade would probably be far less fun than having an occasional few matches where the other team targets the wrong team.