Hero based sr is difficult to implement. This would mean limiting swaps, which goes against the core ideology of overwatch (yes yes hero stacking was a thing but that fully ruined the game back then). I believe it already does compare you with players of your same rank weighted against hero playtime for PBSR, and for MMR it’s based on your own historic performance (from what I remember).
Stats being group based is way too variable to implement. There are times when peeling is not the answer, and sacrificing your support to get an extra kill is more worthwhile. It’s never black and white, so simple stats can’t effectively quantify all the nuance present. Damage during group fights is not necessarily more important than damage outside of it. Say you’re playing tracer and your team loses first 2cp push because they got decimated by a great widow. So you flank after the teamfight and oneclip him just after everyone dies. This would count as damage outside group fights, but is more worthwhile than during the group fight because if you had waited, then it’s possible the widow could have got a pick during the engage. It’s now a 6v5 instead.
A player will generally be the same rank across their mains and the likelihood of them playing other heroes is not too common, so I find this to be a moot point. What if everyone queues with heroes and you’re put into a game where they have a Pharah and you have no hitscan? You’re pretty limited in terms of options.
I completely disagree with your way of matching players. A top 500 with a gold in the same game? That would be ridiculously unbalanced. I hate getting plats in my games because they’re a liability, but a t500 and a gold? People complain that the 1000 SR queue gap is too large, but this is 2000+. The widows won’t teach anything, and will more likely than not be incredibly tilted. Why should higher elo players have to spend every game teaching lower sr players how to play? It’ll get so frustrating after a few games. Not to mention, a T500 would lose more SR per loss than a lower SR player on the same team, so that would lead to a massive increase in smurfing.
It’s not that people at lower ranks don’t want to play tank, it’s that a lot of tank mains have climbed because of the lack of tank mains. It’s easier to climb with other roles (at higher elo) as you spend more time on them rather than competing with other DPS main for a slot, and this leads to better comps.
I can’t comment on QP because it’s useless for me. A tournament mode would be sick though. If also like to see a proper solo queue because that would yield the most balanced matches.