Nerf his healing? Lol what? That's absurd. There's nothing wrong with his healing.
If your team plays together at all, his healing crushes that of all other supports, all while he's happily doing other things (ping damage, booping, speeding people out of trouble). The speedboost is overpowered, sure: It's essential for starting teamfights and enabling ult stacks... but I don't know how you remove that ability and make him still interesting to play.
It's the all-around, low-risk healing and survive that Lucio offers — on top of his decisive speedboost/ult combo — that makes Mercy and Ana sub-optimal picks. (Plus Zen having vastly superior offensive power and a silly cancel ult to boot.)
Reaper, like Lucio, has been slightly and quietly overpowered since the game launched, and has been a top-eight feature of pro meta the entire time (and for a while, when things were tank-heavy, he was a top-four pick). It's subtle, and it's often not noticeable because he gets forced out in some games (usually when the other team has two good ranged DPS who stretch the field of engagement), but his level of self-sufficiency is bananas, and you barely have to aim or do anything to rack up multikills with him.
His average winrate and E/D have consistently been higher than the other offense heroes, his elims, solo kills and final blows have consistently been higher than any other hero, and his ability to isolate and pick off backline targets isn't that far behind Genji's. I often wonder how far he'd outpace all the other offense heroes by if @ReaperNames bros didn't stubbornly autopick him versus the few comps he struggles with.
You could argue that he's one of the few truly "balanced" heroes that has always been effective, but in a world where people are calling for Genji nerfs, people are missing that Reaper quietly does the exact same shit, only more consistently. He just doesn't settle teamfights with quite the same obvious flair, and he doesn't have as high a ceiling.