What is very telling about how Aikman feels about Garrett now is what he doesn't say- he literally never talks about him.
Now go back in time to the mid to late 90's, one of the biggest Garrett fans was Aikman, who called him "another coach on the field" because of his knowledge of offenses and defenses. Ernie Zampese and Chan Gailey were both extremely complimentary of Garrett in terms of his knowledge of offenses and defenses as well.
Fast forward to today, and you see Aikman make no comments about him. Proof of "if you don't have anything nice to say, say nothing at all"
I bet if you could get him off the record with no chance of anyone hearing his thoughts, he'd say without question Garrett is one of the worst, if not the worst HC in the league.