I think that Mack wants conservative play calling, so that is on him.  Some times this helps, sometimes this hurts.  Last year I compared Mack to the big time coaches and he actually wins a higher percentage of games he is favored to win than any other coach I compared him to (I am not sure if this is true after this year).  He also loses more that he is not favored to win than Stoops and Carrol did.  I think this can be attributed to his conservative play calling.

I think that GD does well at offensive scheme and player development.

I think that GD also gets too rapped up in the percentages and this causes him to have poor in game adjustments to teams that throw something new at him and to continue to run plays to reach the balance he wants or that don't work because on paper they should.

Finally, I think that although I would not characterize UT's offense as the best in the nation, with the exception of 2004-2005, it has been, at least statically, in the top 25 for the years GD and Mack have been coaching.

I think the problem here is that GD and Mack have fallen into some kind of common-law marriage situation.  Mack is the (unintentionally) overbearing husband, and GD is the timid wife that just wants to avoid conflict.

I don't think Mack or GD have "the keys to a Vette," but rather they have the keys to two different garages with a couple of clunkers, but overall, enough spare parts for a really smokin' hot rod.  I think that since they've been together so long, GD is more content to let Mack hop in and revise his gameplan.  This can be a good thing, like against Tech, where GD would probably have liked to get into a shootout throwing the ball, but Mack wanted to run JC all day and burn clock - Success.  I think against A&M, though, Mack figured his defense would keep A&M off the field, handed the reigns to Davis, and Davis worked all week on keeping Colt in the pocket, got unlucky on a few dropped passes, fell into a hole, and abandoned the running game.

This is an example of GD's ineptitude.  I think the other side of the coin is in big games like tOSU last year, Mack tells Greg to choke the offense to "protect" the young quarterback, and instead of saying "Well, Coach, that's exactly what they'll gameplan for.  What if we came out firing on all cylinders and took a chance on Colt, then we'd have  a chance to take a lead into halftime, they'd adjust, and we could play defense for the second half?"  Instead of saying that, he doesn't want to say anything and is content to put Colt through the bubble screen boot-camp to get him ready to score one touchdown and lose.

Whether this is actually what is happening, I don't know, but the signs are there.  Who knows?  Maybe Mack is too stubborn to reason with, and a new OC will only get into pissing contests with him for a year and then get fired for some numbnuts that wants to do what Mack says.  At this point, it's worth a shot, though.