I worked for a large company and they had a central training department made up of people who were good at teaching. They would try to learn the subject material before teaching the class. To me, that’s fine when you’re talking about general subjects like Ethics, Security, Safety but not when the classes are technical.
In many instances where a question was asked, they didn’t know the answer. The really good instructors would try to find the answer say during a break in the class or ask for your email and get back to you. Others would just say “I don’t know”.
There were other instances where, for say a new version of a software package, some of us in the class knew more than the instructor.
So, having a teacher teach something that they are not subject experts on doesn’t always work. Now, with football coaches, someone who has been coaching for 25 years should’ve picked up enough football to be able to coach/teach most positions. It still depends on the person. Someone who thinks he’s a know-it-all may not be willing to consult someone who may know more than him.
I think coaching of QBs is specialized. I’m not sure that someone who is a general football coach that never played the position can help a young QB as much as someone who has played the position.