A commonly accepted time frame for mastery is 10,000 hours. I tend to think that's about right.
I'm not sure what you are arguing for or against. 10,000 hours is 10,000 hours. You have to put in your time regardless if it's class, play or solo.
What ever the waza is for the structured class I still get to work on the principle that is my pet project at the time. To extend the music analogy, just because I'm choosing to practice a piece that someone else has chosen doesn't mean I still can't work on tone or color etc. It's Aikido much easier to practice with others. I can go home and do sword cuts and Funekogi Undo, just like I can go home and practice scales.
You seem to see the hierarchy as a yoke that you are forced to labor under, my experience has been people offering a hand up. I guess we both must realize that our experience isn't universal.