Parcells was a great coach but he was not a great coaching hire by Cowboys. He was simply a good one in a morass of bad HC hires.
Greatness = Championships
Parcels was deceived. He was given assurances by Jerry Jones which were reneged later.
I believe Parcells knew he was just going to satisfy his four year contract after his 2nd season. There were issues long before TO.
The lockerroom had always been the Head Coach's domain. Owners and even GM's rarely entered them during halftime. If they did, then they were silent .
When Stephen entered the lockerroom during one halftime, Parcells told him to leave. Stephen Jones refused, saying that he could go anywhere he wanted around the team. Parcells was livid but said nothing. I cite that instance as the point where Parcells realized he didn't have the authority he had originally assumed.
In management training you are usually taught to think of management as a singular entity when it comes to the staff. A decision by any member of management is considered a universal decision of management. It then becomes the responsibility of all management to support that decision whether they agree or not, If they publicly object to the decision it undermines the authority of that member of management and all management in general.
In private, that member of management who made the decision might be advised to consider a different decision under those circumstances in the future but in front of the staff, the decision is fully supported. Parent typically have the same policy when it comes to their children. Otherwise you have a campaign by the staff of "divide and conquer". In other words, dad said no so we will go ask mom. .
This then leads to an attitude of the staff feeling as though they have the right to evaluate the decision to determine if it is correct and actively seeking a reversal if they feel it isn't. This slows down compliance, creates uncertainty, and erodes confidence in management. We absolutely saw this play out during the Head Coaching years of Parcells, Phillips, and Garrett.
Phillips, in particular, was gelded in front of the team, snip, snip. He was not given a defensive coordinator and so that was his responsibility. Additionally, he was not allowed to participate in the offensive gameplanning. The OC, Jason Garrett, reported directly to Jerry Jones. In effect, that made Jerry Jones the Head Coach because both the OC and DC reported directly to him. The complete 2010 tanking was on him.
Such a confusing structure coupled with decisions by committee eliminated accountability and slowed down any decision making. Jerry Jones also insisted on showcasing the team during training camp in order to attract more fans. He volunteered for HOF games, including 2010. He also split training camp into three separate locations in 2010. This contributed to a terrible start in 2010 and ultimately led to Phillip's dismissal after the embarrassing game #8 loss to Green Bay.
The saddest part was the Cowboys had a great 2009 season and were primed to take the next step during a season in which their stadium was hosting the Super Bowl. Very little was spoken about an ultimate goal of playing in the Super Bowl in their stadium. It never seemed prioritized.