Rick is totally self taught, never had a lesson in his life, and had a body strong enough to stand up to shooting many hundreds of arrows every day when he was training.
I don't think either one of us can do that, so we have to find a different way. We weren't born with the genes to be a Tom Brady or a Rick Welch. Face it, you or I will probably never stack 5 arrows into a target at that distance that are all close to touching each other. But what we can both do is learn to improve. You and I are about the same age with the same capabilities (or lack thereof). If you accept a discipline, whether Rick's or Rod's or Arne's, and practice it faithfully every day, you will get to the point where your friends no longer congratulate you on bullseyes, because you make them too often to be worth commenting on.
The thing that makes Rick or Tom special is their ability to be aware, on a physical level, of what their bodies are doing. You mentioned that you were becoming aware of your back muscles. What if you started at that level, and were able to expand your awareness by a factor of 100 or 1,000? Just like you are beginning to be aware of your back muscles where you weren't aware before, you can learn to be aware of all the other things that are important in your shot. You do this by turning off the analytical part of your mind (the part that thinks in words) and focusing on the part of your mind that feels things. It is one thing to be born with these capabilities, but it is just as much fun to learn to use them, even if we never reach the level of those who were born with them, because you can improve more than you ever dreamed possible.