What does Garrett actually DO? I watch him and he just stands there clapping saying "Way to go...way to play." He's in charge of timeouts, red flags, and encourages the team.
Dude, at least two dozen of us board members could do that.
There are some legitimate criticisms of Garrett, but this isn't one of them.
I assume you realize the job isn't just on game day, and that it isn't uncommon for head coaches to not be coordinators. Watch Belichick sometime. He isn't running around coaching players either. Some head coaches do, and some don't. There isn't only one way.
During the week leading up to game the head coach instructs the coaches on what he wants the team to work on, schedules practices, watches game film, reviews game plans with the coordinators and generally oversees game week preparation. He is a manager, much like a manager might be in a business setting where he doesn't do all the work himself, but rather hires lower level managers to make sure the work gets done in accordance with his expectations.
All that said, I'm not indicating that Garrett is outstanding at any of this, I'm just informing that coaching is not just about what you see in game day, and that's especially true with a head coach who is not an offensive or defensive coordinator.