Role Q brings more positives than negatives.
Positives:
No more losing at hero select because you don’t have a decent team comp and the enemy team does
No more going in to play a specific hero or role, but never being able to without it creating an unworkable team comp
No more solo-tank or solo-heal comps, which gets everyone else killed as soon as the solo-tank/healer goes down.
No more being pressured to fill when you don’t want to.
No more having to play as the only tank/healer, which is a often very frustrating/stressful job that shrinks your hero pool down to a miniscule size, burns you out and sucks the joy out of playing.
No more teams where one or more of your teammates is playing an entire elo or more below everyone else, because they’re filling on a role they normally don’t play at your SR… And it only takes one dead weight to lose a match.
No more getting screwed over by your tank or healer (who may be the only tank/healer) swapping to DPS mid-game, and creating chaos with a round of “team comp chicken” where everyone agrees that someone should swap to fill the now-empty role, but no one wants to actually do it.
With role-specific SR, ranking up on ladder will now reward you with better teammates, all of whom want to play their role and are therefore putting in real effort instead. No more resentful fill players half-@$$ing it.
Another role-specific SR bonus: you can branch out and try different roles without risking your SR on your main, no alt accounts needed.
Yet another role specific bonus: if you have a friend who is much higher or lower on the ladder, you can both play together without creating a smurfing session. Have the high-rank player play the role that they genuinely have the lowest skill rating on.
And arguably the most important one of all: With a garunteed workable team comp, you can finally practice a role or hero without constantly getting side-tracked by bad team comps creating stomp-conditions, or having to fill.
Negatives:
You can’t swap roles mid-match
A bit longer que times for dps