I'm going to point out the practical fallacy of your theory.
Most of the people this discussion will be helpful to are writers just starting out. I don't know how much work you've read from writers just starting out. It could be a lot for all I know, but I have read a LOT of first time works, and critiqued them.
The average first time work is garbage, and the average reason it's garbage is because it's filled with sentences you'd swear were written by a third grader. The vast majority of the time when you politely point out the grammar problems which ruin the work, the first time author, who believes in their heart they've just produced "Harry Potter and the Sorcerer's Stone", or "The Hunger Games", or "The Great Gatsby", gets upset with the messenger and goes on to never improve, and never have a chance to find a readership.
So when we get a beginning author who is eager to avoid that trap, let's not tell them that grammar will work itself out. Grammar WILL NOT work itself out. There is a lot of study and work and self-evaluation and revision that comes between garbage and something you can present proudly to a reader. If you don't have a foundation, you won't make that leap in quality.
With all due respect, I see a weakness in your theory as well. You say the average first time work is garbage. That suggests that 50% of first time work is decent or more.
Personally I think people should, and I got into trouble for saying this once before, rely on their education. In that, I mean when you are actually writing -- go with what you got! I can't imagine it is a very creative process if you are writing an interesting story and on the forefront of your consciousness is what form of grammar you should use and what it is called. Perhaps you want to learn that as a side interest, but if you get too worried about it, you may never write, and find out that you are actually in that top 50%.
As a first time fiction novelist, being on this site has been incredibly helpful for me. But when you guys start talking clauses, copular verbs, participial phrases...should I use this structure or that structure..la..la..la, I haven't got a clue what you are talking about. Then I go back to my own work and see that I am apparently already doing what you all say to do.
If someone had said that in order to write well, I need to heed my grammar, I would probably not have started to write my novel. And now I’m 75% complete. Hope I'm in the top 50%.