Do you believe that this is in any way different from the legal profession, the medical profession, teachers, or, well, any other arena?
.... but no one becomes a good teacher after just reaching the "classroom assistant level."
I agree. Dive Instructors are no different than anyone else who chooses to instruct.
I did a six year stint as an instructor at a local college. Ill never forget my first semester, it was horrific. (A whole other story!) However, after that I gained confidence and learned how to convey my skills and knowledge to the future technicians of the world. And I'm proud to say that some actually went on to be the very best.
A good dive instructor does not need to be the best diver in the world, they just need to be able to teach others how to be the best and instill in their charges the desire to continue learning.