Garrett has been coaching his entirely life. He knows (or should know) something about pro football knows what it takes to get to build a a championship team.
However, there are many signs that he hasn't got a clue. He just one of those status quo guys that utter platitudes to the hearts content of the FO and naive fans alike.
He a "coach in training" as what Jerry has mentioned. He should not be.
He also doesn't know his X and Os about football. He should.
He can't adapt or make changes to the playbook. But his the head coach and he should what to do.
Frankly, Garrett is an utter, miserable failure of a head coach. I don't know what value he brings to this team except being Jerry's lapdog.