Quincy may have developed into a mediocre QB in time, but if tou paid attention to his timw in Dallas he was not prettu good. That is why he was called a bus driver.
Parcells taught JJ and company how to run an organization. He showed them how to draft for talent and utilize a philosophy to scout for your system. These things carried over as well to this day. Also let's not forget the drafts he had while in Dallas. MM has a long ways to go before he can shine BP's shoes.
Parcells was terrible at drafting. He basically let his personal affiliation with the Giants affect his ability to coach. Drafting Carpenter as LB in the first round was dumb. Also, trading out of the first round when Steven Jackson, best running back in the draft was a dumb move.
He also wanted to draft Marcus Spears first over Demarcus Ware. Luckily, Jerry stepped in and took him. Otherwise I can see D. Ware playing for another team.
Parcells was good with getting the Cowboys house in order. But when it came to acquire talent and drafting players, he was terrible. The Cowboys was nothing more than Parcell's rehashed Giants team.
Heck, he even forced Mike Zimmer to run a 3-4 defense and scaled down Sean Peyton's playbook.
At least McCarthy let's his assistants doing the dirty work. While Parcells forced his assistants to do it his way.
Thus I think McCarthy is a better coach than Parcells.