In the TB/BB era, the Pats have played in 7 Super Bowls (so far). I think you can say that they played against top-echelon (call it top 10ish) QBs in six of them, with the one exception being the game against the Panthers. Until this year.
That said, their road to the Super Bowl over all 8 years has shown a larger percentage of lower tier QBs, but it’s been a rare case where said lower tier QB has put up a stinker.
Brockstar last year is about it.
Maybe Mariota this year.
Oddly, there have been more stinkers put up by top-tier QBs than bottom.
I’d love to see that reversed finally.
When you play against a top-tier QB, you take away their strength, and game plan for that QB. If you're winning that game, almost by definition (particularly with the take-away-the-strength mantra of BB) it means that the excellent QB will have a sub-par game.
When you play against a lower-tier QB, you take away whatever else is it they do and dare that mediocre QB to beat you in the pocket, through the air. Focus on stopping the run (a team with a mediocre QB almost certainly has relied on the run), and contain (if the guy is a scrambler). Thing is, if the QB is mediocre-to-good-ish, he'll get his (especially with the Pat's philosophy of bend, give up lots of plays but avoid the big bombs, make them make a lot of plays, a lot of passes, and stand at the red zone), and so it won't be a stinker. (if the QB is bad-to-Tebow, well....).
So, the situation you describe isn't that odd.
edit: They will look to make Foles beat them through the air, unless/until Foles shows that he can do it consistently. Not once, but over and over. If Foles comes out and looks like peak-Manning (Peyton) and the score a TD on their first drive, don't look for the philosophy to change, unless he's been on fire well into the 2nd quarter.