Get out of voice chat and stop looking at text chat. Then play whoever you're good at and enjoy the game.
The only times I lose massive amounts of SR is when I flex play and choose whatever hero these braindead idiots tell me to play.
Everyone's experience in the game is different... your Mei could be asking you to go mercy because she's being targeted and dying a lot and wants the rez. But your orbs of discord may be 50% of the reason your team is getting kills. So switching to mercy would hurt the team but help your Mei. Overall that's a downgrade.
So play who you're good at. F them