It is hero dependent but most hitscans are really easy, or I should say, simple.
Genji any season is more difficult to master than any hitscan outside of Tracer. (which isn’t really a hitscan hero anyway). The value you speak of from his passives is only a thing at low rank and should not be in the same sentence as “mastering a hero.”
For hitscans there is a heavy emphasis on mechanics and less on others. Sure, you need to have a good understanding of the game but that is universal to every hero. The ability to pressure an enemy at range is a massive advantage in offense and defense, as opposed to flankers who are guaranteed to be in enemy kill zone when enemies are in flanker’s kill zone.
Widow pushed Genji out in a dive meta, a meta that should be as favorable to Genji as it should be unfavorable to Widow.
Your statement would have a shred of truth had Genji or Tracer pushed Widow/Hanzo out of double sniper meta. Neither did. Sombra, Doom, Reaper, none of the flankers could challenge double snipers in double sniper meta.