Based on everything we've heard from Belichick, Butler, and multiple sources (including players) close to the team, it wasn't anything significant at all. It was for match-up reasons. Which is mind boggling. The GOAT coach cost his team their 6th Super Bowl victory and essentially flushed an all time great game by his quarterback down the crapper.
you're overselling that quite heavily. Remember, everything was falling the Eagles way LITERALLY ALL GAME. You can't just assume that a substitution of a player who was sick and had been struggling for weeks would flip the script. It's a possibility, but again, if it was about talent, the Patriots win that Superbowl. The Eagles were getting WAY more than their share of bounces and football luck.
I don't even object to the point you're making, so much as the certainty with which you're making it. Claiming that THE PATRIOTS WOULD ABSOLUTELY DEFINITELY WIN THE SUPERBOWL IF BUTLER HAD PLAYED is an overstatement. It's accurate to say that the odds are better, and with the game on a knife's edge, it might have been a difference maker. I honestly think that's the absolute most you can say.
Pretending that the entire difference between victory and defeat is #21 playing isn't necessarily wrong, but it
is stating the case with far more certainty than it actually deserves.
As an aside did you SEE the look in Nick Foles' eyes? He had a look in his eyes in that game that I've only seen on one face in my life, and that face stands over a #12 Patriots jersey. I'm not sure the 85 Bears or the '15 Broncos would have stopped Foles that night, he was Brady-level locked in. Not like you'd expect it from Nick Foles, but for some reason, on that night he was the best quarterback in the world.
The Vikings had a far better defense than we did that year. Foles absolutely DESTROYED them. I don't think he was ever at that level before and probably never will be again, but when a guy is dialed in like that, you can't assume that ANYTHING would stop them, even things that normally would. I honestly think we did very well to hang with that team at all, considering. We were the only ones that came close to stopping them.