I played AP and randomed in all 10 of my solo matches and lost 9 of them. I started legitimately picking after I got landed at like 4600 (which is pretty high for a 10% winrate in placement, if I do say so myself) and won 4 or 5 in a row and went up 100 rating and was already bored and stopped. I play party with friends from time to time, as you know, but I don't really take it seriously at all because party MMR is even more of a joke than solo.
I don't know how much you know about MMR manipulation, but I've seen you recognize the fact that people do it at least. I have a friend at 6200, and you know what he does? Every time he has a bad week/day/game and drops below his pretty designated number he has one of our other friends log on to his 6k alt, queue up, and throw games to get him back up to where he was. And I know he isn't the only person that does this. It's not as abusive as party MMR stacking, but it's still easily possible and you can still be boosted to 6k if you ask the right people.
And I was going to wave my 6k MMR in everyone's face but I got bored of climbing the ladder the second I started. I barely play this game anymore to be honest, it's hard to stay interested in a game when you have nowhere to grow, in my opinion. Just playing to play isn't enough for me, sadly, though I do like the hats quite a bit.
If you really want me to, I'll go pay someone for a 6k MMR account if it will shut you up for a while. Even if I couldn't get there on my own, it wouldn't matter, as it has been shown repeatedly that staying at an MMR level is a lot easier than getting there, and even if I was only a 5k player I could probably keep a 6k MMR pretty easily.