As long as you queue solo for a match and in a given role, I think it is correct have rankings separated by role. Healer, Tank, melee, and ranged dps. 4 roles, 4 rankings. Making all roles together as it is now, dominant roles problem is what happens next.

I don't think healer need nerfs, because healer role always had been key for any pvp. How deal the healer is one of the basics of any team discussing tactics. Let the healers battle for ranking between them.

Role separation is also more fair, because we can see a player on which role s/he is good at. Godlike players will be on top 10 of each role, kudos to them, but a great healer may also be a shitty dps player and it is correct s/he stay only on healer rankings.