the Overwatch team has already said they aren't going to do this for fear that players will attempt to "game" individual statistics, and focus less on winning. I understand their concern, but is this trade-off really worse than the incredibly toxic community we've ended up with, with leavers, trolls, etc. in a large percentage of matches, and a large portion of the community believing that their rank isn't representative of their actual skill?
If individual performance were included in assessing one's gains and losses after a match, the problem of players picking only their best DPS might actually get worse. People wouldn't actively throw a match as frequently, sure--if their performance matters, they'll be trying to get kills. But they still won't be contributing to a team effort.
Add to this the difficulty of balancing exactly what kind of numbers are important for each of the twenty-five characters in Overwatch, and you'll see that implementing such a system is far from a simple proposal. Some heroes work well solo; they'll get reasonably high numbers even without any team cohesion. Players who pick those heroes will end up advancing, while those who try to help the team will fall behind. You typically won't have very good numbers as a tank if your team isn't working together, because you'll be dead too much of the time. I've seen tanks in good teams end up with gold damage. I've also seen people who I know are excellent tanks get crap numbers because half the team is running around like spastic chickens.
I certainly think I could do better than my rank has been the last two seasons, and I often fall into the trap of blaming my team for a loss. (The highest I've been is barely over 2000 in the two sesons I've played. I haven't started my placements for the new season yet.) People very often think they're better than they really are, whether it's at Overwatch, at driving, or at picking up [insert gender of choice here]. Sometimes, you think you're better than the rest of your team, and you really are. Sometimes, you're really not.
So every time you see "ELO HELL", take it with a grain of salt: If everyone in Gold really deserved to be in Platinum, and everyone in Plat really deserved to be in Diamond, uh... wait. Then who would be left in Gold? What would that mean about the people already in Diamond? Does no one deserve to be in Bronze? Are the GM players just really lucky? Or maybe only the people who are better than everyone else ever talk about their woes, while the crap players who lucked into Plat just keep their mouths shut, hoping no one will figure out their deep, dark secret. Hell, if I luck into Plat this time around... I'll probably quit ranked until next season. Maybe yell at everyone in QP about how they suck because I'm in PLATINUM. Ride the high for a while, y'know? :P
And then I get ganked repeatedly by a Bronze Reaper