The truly difficult thing about Ryu was never the inputs (though they are quite annoying for those unfamiliar, it's certainly not an impossible hurdle to overcome).
What makes Ryu hard to use, and I can see why people might abandon him even though his potential is through the roof, is that you have to master a Street Fighter-esque understanding of footsies and neutral. You have to use all of the tools at his disposal to play a versatile and scary but more or less honest neutral game. The light/heavy inputs basically mean that he has more tools in footsies than anyone else, but not one tool that will just overwhelm the competition like Sheik fair.
https://www.youtube.com/watch?v=3UaXhe_XPsU
Watch this Ultra SFIV final. Of course, it's a different game and movement in general is different when you can't run, have no double jumps or platforms, and you can't walk backwards without turning around (unless you crawl) but it is very rare that I see Smash players approach this game similarly.
He moves differently, demands you pay attention to things like spacing, but a lot of players of the character have mainly concentrated on his combo potential. "IF I get in, I can do this!!!" This reminds me of that Wobbles article people have been posting about local maxima. I might even argue that people have focused on his combo game at the expense of developing his neutral.
Now compare all of this to Bayonetta. People argue that she's SUCH a different character compared to other Smash characters, but they're mostly concentrating on the nature of her combo game. In terms of movement, she's a lot of what people look for in a Smash character: someone who can zip through the air and ground a bunch, and whose strong mobility comes from using a lot of big movements. It's not just that she's easier to win with (still debatable), but that, as much as we say her neutral is only okay, she fits the general Smash player's idea of neutral much more.