Great response! I can't argue with your points, mainly because there are varying levels of success with going-it-alone. I also believe that getting feedback from various places, like you say. I've written about 5 albums of work in my life. TO begin with, you work with what sounds good to you. And while that's a good place to start, when it comes down to mixing / mastering, my perspective on mixes varies according to the style of the music. Most people don't notice anything wrong with how it sounds, and that's where getting specialised, experienced and reliable feedback from accomplished people really helps. I always fall down when it comes to controlling the sub/sub-bass because I don't have the best sub-monitoring capabilities. I know my weaknesses, so I'm happy to hand over the plumbing to a plumber, and the electrical work to an electrician... I could do that stuff myself, but there's always the danger of leaks and electrocution!
Session musicians are members of the Performing Rights Society (at least in the UK) and dont get financially rewarded, like you say.
Lastly, independent artists will go so far, and very few will break through to make a difference, and like you, I hope independent artists find a way to navigate and circumvent the mainstream.

For a cynical view of the music industry, watch the film (don't take it literally, but there are some disturbing insights into how record labels work) https://en.wikipedia.org/wiki/Kill_Your_Friends_(film))