Well I don't know about the learning curve, if you mean knowing what everyone does, it goes pretty quick, it's only like 1/4 of LoL or Dota hero pools and the heroes have less skills too. If you mean actually learning to play every hero, then yeah it's long but you'll most likely stick to what you like. The great part about having so many is you don't get bored as fast and you can find something that's very specific to your tastes, rather than a more generalist approach like support > medic in TF2. Some heroes have higher learning curves than others too. Like for example Hanzo and Genji take a while because they have some weird quirks, but others are fairly straight forward.
I've played the game I don't know, probably 100ish hours or so? And there's still a bunch of heroes I've never played an entire game. I think I've never picked Widowmaker even once other than a skirmish while waiting for another game. I don't think I've ever picked Junkrat. Was the same in dota/lol/hon/hots and so on, some stuff just doesn't appeal to me so I don't even bother with it. There's enough choice with the stuff I like.