Yes...common
No...they NEVER do anything about it.
Definitely...self perpetuating.

Recently, my flying has put me on American a lot. So, I've had the chance to notice this. Exactly as the OP says on AS...first class, MVPG - hardly matters. If you're not AT the front during the 30 second window that priority boarding is called, you will be boarding in the last 1/3 of the group!

On American, as MVPG, we get no recognition, no priority whatsoever. I am usually assigned in one of the later groups, it seems. To my amazement on my first recent American flight, the pax were actually waiting for their group to be called before approaching the gate. In fact, group 3 could be essentially finished boarding, and the line would trickle out completely, and pax from group 4 were NOT storming the gate. It was very organized, and went very smoothly. First class and elite passengers boarded comfortably, and had plenty of opportunity to come forward. I actually noticed GA's turning pax away that were not in the appropriate group. This process was repeated on my several AA flights over the last couple of months, and on a couple of Delta flights recently as well.

Why can't AS change its ways? It is so much smoother...and I'd dare to bet the boarding process is quicker as well!

This is not rocket science. In fact, AS would not have to change their policy even one bit - they don't need groups or any such thing. They simply could begin to enforce their existing policy and board in the order they currently pretend to board...leave a little time between each group...and turn people away that were boarding out of turn.