He's not. I play around upper 60s/low 70s in comp on PC. He's very good and very punishing, but in a more coordinated environment he's a lot easier to deal with.
It's really easy for Genji to snowball a fight out of control, but it's also easy for him to not get a chance to do that. There's a reason he gets switched a lot.
He's just high skill cap to play and high skill cap to counter. I'll admit he's much better in solo q where teams have a harder time coordinating against him, but if balance starts happening based around that then we're in for some sad times.
I think it's a bigger problem on PS4, I've noticed a ton of Genji players recently and it's extremely hard to pin him down (doesn't help that he distorts his body so much with his double jump).
I've actually been trying to play him more because of that, maybe help predict what other genji players do once you see a bunch of scenarios through their eyes.