Think about how much you lose, though:
The quick Hammond-swap to get to contest a point.
Mei to stall.
Overall creativity. Say what you will about GOATs, but there were people who actively came up with that style of play, and it worked. Then there were people who refined it.
I get the impetus to go for 2-2-2, because it allows for the most variability in comps, but what if there were some brilliant idea to combo 3 DPS abilities? How much pressure does it put on the decision what role a hero belongs to? Zarya and Bastion are both tanky and highly damaging, yet one is a tank and the other is not. Rightfully so in my opinion, but where do you draw the line? Even Brig is sort of a mixture of all 3. Symm was a support for a long time, and people still made arguments about why she actually belonged there.
And then there’s flexing - which is something the devs always intended to be part of OW (little did they know…^^). I’ve had multiple games where I’d play tank on attack and support on defense, because someone else swapped the other way round. What if that’s actually feasible? What if you want a specific comp to counter the opponent - say, you need a Rein, but your Winston who queued as a tank can’t play Rein. He could play Lucio, and the Ana could play Rein, but how would they swap? Of course they don’t have to, but Blizz wants people to be able to.
And then there’s the logistics. Think about it mathematically: say you have 40% queueing as DPS (low estimate, I think), 30% as tank, 30% as support. We start with the first minute of a season, 100 players - 40 DPS, 30 tanks, 30 supports. We get 15 games with 2 of each, 10 DPS mains wait.
The next minute starts, we get 100 new players. Again they form 15 new teams, 5 of those gobble up the overflow of DPS from the 1st minute - they won’t mind, waited only for a minute, right? But now we have 20 people queueing as DPS while everyone else is already in game. 3rd minute, 100 new people - we can have the 20 DPS get into 10 of the 15 games, but now we have a stack of 30 DPS mains still in the queue.
You can clearly see: it doesn’t get any better. The queue times won’t get any shorter, only longer. Unless you get a consistant 33.3% queuers for every single role, there will be an avalance for the waiting time. Sure, supports and tanks will find a game in 3 seconds, because there will always be so many DPS waiting, but the only way for it to ever regulate is for DPS mains to go “Hell no, I won’t wait that long!” and queue for a different role or a different mode. In other words, role queue would mean that the most picked role - and that is DPS, considering how Blizz keeps on dumping on the other roles - will be forced into a game of patience.
As for stats: sure, if you look at overall comp pick rates, tanks and supports come out ahead, but that’s not because people choose to play them, but because people flex to them. With role queue, there would be no “I’ll join the game and if noone else plays tank, I can do it.”, it would be about “I want to play THIS.” You know, like in QP, where tanks have a total pick rate of 24% (supports: 31%). And even those numbers might be skewed by the “Uggh, I don’t want to play in a 6 DPS comp.” crowd that still swap.