No one is saying "only". Defense was inconsistent and special teams was horrid per par. But the great QBs, the top-of-the-market QBs, win "in spite of". Mahomes, Wilson, Rodgers, and Brady have won "in spite of".
Dak Prescott wins games "because of", as opposed to "in spite of". That's why he's not a 35+ million dollar QB, unless some bottom feeder wants to pay him that and enjoy winning 6-8 games a year with an average QB being surrounded by lesser talent due to the salary cap.