Some comparison points:
Peyton Manning: 27 playoff games; 11 were below 80, and 5 between 80 and 89.9.
Eli Manning: 12 games, 4 below 8, and 3 more in the 80's.
Russell Wilson: 12 games, 4 below 80
Ben Roethlisberger: 19 playoff games: 9 below 80, and 1 in the 80's.
Drew Brees: 11 playoff games: 1 below 80, and 2 more in the 80's.
Aaron Rodgers: 15 playoff games: 4 below 80 (none in the 80's).
Julian Edelman: 158.3 career playoff rating
And some comparisons to the historical greats:
Joe Montana: 23 playoff games, 6 below 80, and 3 between 80 and 89.9.
Brett Favre: 24 playoff games, 8 below 80, and 4 in the 80's.
Troy Aikman: 16 playoff games, 7 below 80 (none in the 80's)
John Elway: 22 playoff games, 9 below 80, and 4 in the 80's.
Dan Marino: 18 playoff games, 10 below 80, and 2 in the 80's.
Tony Eason: 5 playoff games, 1 below 80
At a quick look, Brady's percentages of "bad" games in the playoffs is not at all far from either the current top tier QB's or the historical greats. Sure, by some measures, Wilson, Brees, Rodgers may look like better "playoff QB's"; but none of them have played in half the number of the playoff games as Brady, so I'm not sure that would be a valid conclusion.
There were also 6 playoff games were Brady was sacked 3 or more times; he's 2-4 in those 6, with 2 of those losses including his 2 worst games by rating: the 33-14 blowout loss to the Ravens in the wild card round, and last season's loss to Denver.
BTW, cutting or trading Brady in 2017 would result in the Pats taking a $27M dead money charge, so yeah, Cowherd is just throwing crap up there to get some clicks.