the only reason why you will think a flat SR system is good is if you always think you belong higher than where your MMR currently has you.
a flat SR gain/loss will essentially become a mode where if you play enough games with a 51% win rate. you will reach GM.
simple math.
the entire point of this idea is that you think players who constantly plays should CONSTANTLY be gaining SR.
a bronze player can literally reach plat/diamond simply because he plays a shit ton more games and has like a 55% win rate.
his MMR/skills is no where near that of a diamond player but because of a SR system based around how much time is put into the game. anybody with enough time can do it.
you realize MMR benefits you right?
if you right now lost 15-20 games due to bad teammates/bad luck. your MMR will not drop as fast. you can gain back all that SR within like realistically 10-12 games.
MMR is there to help you. the only reason why you will want to gain/lose the same amount of SR is if you are currently losing more SR than you gain simply because your MMR is too low for your SR.
nobody in the right mind would want to have to win 20 games in a row just to offset 20 games of bad luck especially when the game currently can do that in 10-15 games.
It also becomes impossible for off meta one tricks to abuse this system since they would have to play together with their team in order to win and climb at all.
this already doesn't happen. stop assuming blizzard compares the stats of someone who plays tracer for less than 30 seconds to someone who plays tracer the entire game.
the system most likely compares your stats based on average stats per death or in a time frame so small that its possible to compare two players playing the same hero of drastically different time played. otherwise if you decide to pick tracer to contest over time. your SR will tank when you inevitably die without getting a kill or much damage.
we all saw the bastion video. the guy was first off an actual GM player. he wasn't some gold player one tricking bastion to reach GM. and he had like a 53%? win rate. that's normal.