I think Garrett knows how a team should be run and should be built, he just doesn't exactly know how to do it on gameday. He wants a tough, run-first team, but he doesn't know how to adjust or play off of that, i.e., the fact that we ran like 80% of the time on 1st down for weeks before we started going play action off of it, trying to catch teams selling out against the run.
I think he helps to bring a sober voice to the front office during the draft, when constructing a team and so forth, so that helps when Stephen or whoever is trying to keep Jerry from going off the deep end, but on gameday I think he freezes up, tries to force square pegs into round holes and lacks even an ounce of creativity.
I think he has the book smarts but no actual operational ability as a coach, basically. He would probably be better off working in a front office where he has the time to make logical, thought out decisions rather than having to make snap decisions on game days.