I don't believe Garrett sabotaged Wade for several reasons. I'll stipulate that Holley (and Patrick Crayton) is telling the truth about a new playbook after Wade was fired.
1. Jason probably had to have Wade "approve" his playbook, as Jason respects the hierarchy of the coaching staff (which is clearly a detriment this year). Jason has talked about this many times (not the specifics of Wade getting fired, but respecting the hierarchy within the coaching staff). So when Wade was fired, he could run everything he wanted without Wade's sign off. Things weren't much better even if they were "different". They racked up some points and yards against some bad defenses. I mean, Tashard Choice (!) had a 100 yard game vs. Indy (Felix had 83 in the same game).
2. How does Garrett sabotage a defense that had given up?
3. How did Garrett sabotage Romo getting his collar broken?
4. In Wade's last 5 games, the Cowboys scored 27, 21, 35, 17, 7. The defense gave up 34, 24, 41, 35, 45. That's on Jason how?
5. Jason Garrett is a day2day, "follow the process" type dude that doesn't seem to have any long game in him other than the ability to evaluate offensive talent. He's not the "If I sabotage Wade, I'll get the HC gig" type of thinker. He's too thickheaded.
Garrett has always been a mediocre coach that needed healthy, elite talent to win.
The irony is that his best coaching was probably those last 7 games of 2010 where he went 4-3 with a back-up QB. Usually with a back-up QB Garrett is awful and conservative (not including 2016 which was a different case as they had Peak Zeke, Peak OL play and WRs at their Peak as well). With nothing to play for in 2010's last 7 games, the Cowboys offense was very, very productive with a back-up QB.
Bye, Garrett. Your mediocrity and stubbornness won't be missed.