Everyone pays lip service to football being a team sport, then turns around and blames the QB for everything. It's a baby's idea of how football works.
And the 2007 Cowboys were #13 in points allowed. People keep talking about that D but it was extremely average. 2014 they were #15 in points allowed. 2009 was the closest they had to having a real championship defense, but they imploded against the Vikings along with the offensive line.
For reference, here are the scoring defenses Brady won Super Bowls with: #1, #2, #5, #6, #6, #8.