Sure the execution of moves are harder but at its lowest level you don't even need to pull dp's off reliably. People have been playing fighting games for decades very casually with their friends, by effectively just 'button mashing' and still having fun. The issue is, you don't really get that level of play online.
Unlike in DOTA where you do have levels of play where people don't really know what they're doing.
I think you'd be surprised how decent the matchmaking is in Dota 2 really. I only started playing last year, and although I did have friends who already played. I didn't want to always burden them with my lack of skill/knowledge, so I played solo quite a lot. I always got matched with people who had a similar amount of time playing. Some people didn't seem to understand any of the mechanics, others probably played LoL or whatever before as they had more of a grasp, but over all it was a pretty good place to learn. First few games there was a few smurfs, but they get weaned out by the system.
Oh I don't disagree that people solo queue period, I know I do that kind of shit all the time, but I do think people don't get into these kinds of games without friends to play with. In a one on one competitive game that's a lot less likely - your friend being miles better than you is frustrating rather than encouraging, only when you're very close in skill is it a solid motivation for most people to keep fighting each other and getting better. With something like Dota we can play a few games, you can encourage and tell me what to do, and then if I'm trying to improve to keep playing with you I can solo queue when you're not around. It's a very different dynamic.