It’s Reaper and it ain’t even close.
Widowmaker has seen consistent high tier play over the years, her recent(ish) range nerf only illustrates how long it took for any of them to have an effect on her. Which she’s been buffed since new Sombra throws pocket sand in her eyes.
Cassidy only really had his mag grenade and hp changed. His more annoying to play against then underpowered. Same goes with Symmetra and Mei.
Junkrat loses value the higher you go but that’s more on him scaling to his competitors who can hold their ground, out damage him and exploit his more linear movement. If he can work past or around that his fine.
Pharah… wasn’t there a streamer who reached top 10 on 10 alternate accounts playing Pharah? I get she’s more boring then a paint drying competition. But her kit has high burst, strong mobility and great crowd control. There’s a reason she forces hitscan on the enemy team and it’s not because she’s weak. Echo maybe a flying hero done right, but Echo’s range is more limited and works best as a dive hero.
His not even a good tank buster. Sustain and other higher damage sources can do more and at better ranges then he can. He can’t fade out of abilities like he could in Overwatch 1, his ultimate is still bad (only real upside is the healing) and there’s enough you can do to negate him getting value you don’t need to swap.