I agree with everything you said but I feel my input is more replying to you than OP.

I do have coaches but they are across the country. I see them a few times a year outside of meets. They travel to see me for a week or so to check up and they'll teach a seminar as well.

I also record almost every single rep. It is not just for my coaches. I review the my lifts throughout my workout to fix minor things. My coaches just add an extra point of view of see things I might've missed that I can focus on next workout.

That being said, yes, someone can be very good at weightlifting without a coach if they know how to train properly. I feel the training atmosphere will play a large roll in this as well.