I'm pretty adverse to nerfs/buffs, because it's almost never right on the money, even after multiple passes. See Tjorb on PS4 and Zen across the board.
But if a single character can be played at any level and consistently get medals, even healing ones, like Reaper can, it may be time to see why his efficacy is greater than most other characters.
Genji is a harder case, to me, because at low skill levels, he's an absolute joke. But at high ones, he's an absolute nightmare. You can't balance people's playing skills, so I'm not sure what the right answer is with him.
My inclination would be to say buff Winston, but he's got such an incredible skillset that he could get out of hand pretty damn quickly if he were buffed. The selfish side of me really wants to see him get buffed, because he's my go-to character for when I cross/blow right through that line of "just drunk enough."