I guess the Falcons made those moves because the defense struggled for most of the season and the collapse in the Super Bowl was only tipped the scales.
A few thoughts on that.
First, it's ultimately Quinn's defense. So it would seem like those guys are just scapegoats, if they are indeed being let go because of the defensive performance. I'll say again, there could easily be more going on.
And secondly, the defense struggled but also showed obvious signs of improvement. 5 of their final 7 opponents scored less than 20 points. They held the Seahawks and Packers to 20 and 21 respectively. And they really reached their crescendo in the SB with an impressive performance, but the offense couldn't pick them up.
To start the game, New England went Punt, Punt, Lost Fumble, Punt, Pick 6, FG, Punt.
It was on the Patriots' 8th drive that they finally scored their TD to get to 28-9.
From that point forward, the Falcons offense went Punt, Lost Fumble, Punt (after 1st & 10 at the NE 22), Punt.
Their offensive ineptitude forced the defense to be out there for 93 snaps. No defense can hold up for 93 snaps. That's basically a game and a half.
In short, I'd say it was the offense that collapsed.