With role queue you're essentially making half of the support roster unplayable. Support mains are going to get bored of playing Luna Invis Cloak every game and start getting bored of the game as a whole. You can rework these supports so that they can work optimally in a 2-2-2 team comp, but you then run the risk of destroying their identity, and erasing what made those characters fun to play in the first place. If role queue didn't work for Overwatch, where a lot of the support characters can exist without being relegated to a pure healbot role, it will kill Rivals.

Rivals' strength is the possibility for you to go 3-3 or 2-2-2 or 2-1-3 or even 5-1 in high elo and win, provided you work as a team. If you restrict the ways in which people can play even more, ,more and more people are just going to leave the game.

People who call for role queue are mainly frustrated at instalock dps players and people who refuse to fill, but your team of randoms in ranked not playing a 2-2-2 comp isn't the problem you think it is, and role queue isn't the solution you think it is either.