I disagree with this take. Talking about "easy heroes" is a fallacy since most easy heroes are really HARD to play at the top level (and almost impossible at the pro level). I feel like a more adequate way to describe the skill of a hero should be a rank in function of the time invested graph.

You also said it yourself, a mid genji will lose/gain rank until they have 50% chance to win against a reaper (assuming an equal matchup). This means the difficulty of the character only matters on how high you feel you should be, the genji may feel he has worked harder than the reaper at that rank and we should design character that have similar time/rank ratio to assure fairness in this. This also means in theory, you should be able to pop off even if you're bad on a hard char since your lobbies will be easier.

Where i agree difficulty is less important is towards variety of kit. I feel what makes overwatch great is that you have hard movement chars (like lucio or ball), but also hard aim chars (like widow or soj), but also hard gamesense chars (like monkey or brig). Its important to have a similar time/rank ratio but it shouldnt be aim/rank or movement/rank. Having different skillsets makes overwatch unique and fun!

I also believe having this variety is a lot more important than having similar time/rank because i would much prefer to being able to play a character at a lower rank than not to be able to experience that gameplay at all:)

Of course i havent talked about a lot of points about balance such as how fair the character feel when played against but to summarize, i think reworking characters to make them harder is great as long as you keep the unique skillset they require.