My big thing is I don't personally feel he makes players better, definitely not the sum of their parts. He make them more disciplined or organized, but I don't see the product on the field being anything additional to what the talent is capable of.
I want to like the guy because he represents stability, but his output, his treatment and handing of adverse situations, particularly with regards to selling out his own hires, I just don't see it. Finally I am a big Romo fan and I would have loved to see him with a Sean McVay or Shanahan type (sure that's asking a lot) as offensive coordinator or head coach, but definitely at least at o-coordinator I would loved to see Romo w/someone that had actually earned the job rather than be Jerry's handpicked Superbowl 90s reminder.
In other words, I suspect if Garrett was not a part of those teams he would have actually been forced to work his way up the ranks and get better as a result...it is a process after all
but as it stands I think he was gifted a job he didn't earn, and he hasn't shown me personally anything that says "oh, well I see why they tabbed him as the next thing"