I played Mercy from day one until I bottomed out at 900sr. I could play Mercy at a solid 1200sr once I was in the swing of things.
I had to take action and start playing DPS, never understood what a tank really was. Especially without “threat” like in WoW.
On DPS I made it to 2350sr, but could play at a solid 1950sr level.
These are the things I am actively doing to improve my SR: I try to click the buttons faster.