I've come to the conclusion it's really impossible to judge Jason Garrett. True, he's shown nothing to indicate he's a quality NFL head coach. Several coaches fired last week could coach him under the table. Many high school coaches appear to have a better grasp of what to do with timeouts and managing the end of a half better than Garrett does.
But to dismiss the Jones factor is foolish. No HC is going to succeed when someone else is deciding: who the coordinators who are, the system the defense will run, which players will play, what players are on the roster, whether or not the offensive gameplan will feature running, who is in the lockeroom berating injured players or giving pep talks, and so forth. Or goes on the radio or TV constantly to remind everyone who is in charge, and what the strat for next weeks game should be. Or comes down to the sidelines to tell him who to take out of the game.
My belief? Jason Garrett is absolutely miserable. He looks like a zombie on the sidelines and in press conferences. The last place he wants to be is coaching in Dallas as the pseudo head coach, while Jerry Jones is the walk-around head coach. He'd love nothing more than to get out of Dallas and get an assistant job elsewhere.
Why doesn't he just walk away, then? Because most people can't (or wouldn't be able to, given the opportunity) bring themselves to walk away from a salary that is probably in the neighborhood of $5M a year. He was probably praying that Jones would fire him.
As Jimmy Johnson said a couple years ago, Jerry Jones fancies himself the head coach. Garrett handles the little things Jerry doesn't want to fool with while he's busy promoting concerts, bowl games, boxing matches, making commercials, etc. Since Garrett isn't really a head coach, Jones doesn't really evaluate him as such either. Really, there's no way to evaluate Garrett any better than it was any of the long line of sad sacks fired by Al Davis.