So, to the OP, yes it is possible. I would argue that someone who put as much time, effort and money into a subject as you have would get better without any training. Dumb luck, as it were, and lots of effort would probably yield similar results. The problem is, most people don't learn like you, or have the time or commitment to the exclusion of other things in their lives.
I think you're an outlier and your results are not applicable for the vast majority of folks, for a number of reasons.
Comparing shooting to other top level sports, we almost never see professional athletes that have not received in-person coaching and evaluation. Why is that?
GJM noted an important point about the pandemic as an experiment in distance learning the last few years. It has been disastrous for childhood development. However, in that case we are talking about less-motivated subjects and oft-times poor instructors, so it may not directly correlate.
Perhaps, if I watched a number of pornos and worked on my technique, I could become the lothario I've always wanted to be.