What you need to remember with these D1 pitchers who are now pitching coaches is the intangibles they bring to the lesson. Knowledge of the game, pitching strategies, how do/did they prepare for the game, passion for pitching, ability to relate to a girl as a female, how to field their position, shared experiences when they were learning how to pitch, competitive fire, etc.
When I used to coach, I had a couple of former UCLA players run a two-hour practice and the girls absolutely loved it.
While proper pitching mechanics are #1, don't discount all of the other factors that elite athletes bring to the lesson.
I completely agree that the first-hand experience that former high-level players bring to the table is very valuable, and can be highly inspirational for young players. This reflects a lot on their quality as a teacher, and how well they can communicate their experiences, knowledge, and passion to their students. However, when these experienced, knowledgeable, and passionate teachers provide instruction that is flawed and doesn't match what they actually do/did, it can spoil the soup.