actually, there are different things when you are learning a hero, what you need. at first, it is more about you and hero - other players don't matter. you need to learn how talents work, if there are delays, how long are skill shots, how big your hero is. how well do you contribute at clearing lanes, doing camps, doing bosses. for all that, AI is good enough.

then, you need to learn how that hero interacts with other heroes. how much dmg you do, how much you can take, which is good sequences of talents you use, how hard are those skill shots you use to land against real players. for all that, QM is good enough. it is also rather good for nova especially, because if you can't clean up in QM, you will for sure not be able to in HL, for all that where team play is even more important. unrealistic composition? for nova to be good for composition in HL, well, that is rather unlikely.

then you go to hero league, where you are supposed to play your best. is your best at new heroes? people with basic understanding, as you put it, are picking new heroes for HL all the time, well, good for them, bad for my ladder points. i know, no one cares in HL right now. see later tonight when people will take random heroes to your HL games and it will not be even for them to learn, it will be because they have quest. that is the state of HL right know: people learning new heroes, people not caring, people doing quests (while picking what is bad for the team). is that what ranked play is supposed to be? sure, unranked draft would be nice for this. but just because we don't have something like that, i don't see why you would need to be that selfish and do what you want, because you feel like it.