First off, I highly doubt Eagles make it to the superbowl if Wentz goes down in week 9. Wentz and the eagles pretty much locked up everything prior to Foles stepping in.
Secondly, It should be obvious that this year was more of a nominally that those teams made it as far as they did with the QB's they have. I agree that it is a team game, but it so much more difficult to build and keep a defense like that together.
You said that you want to actually win a superbowl, well history has shown us that majority of the time, if you want to win a superbowl you have to have an above average QB to win it all. And usually before a team wins a superbowl they have several playoff appearances prior to winning a superbowl. Teams we consistently make the playoffs have top tier QB's. And the ones that don't, don't win superbowls (Most of the time). It increases a team's chance of winning a superbowl with a top tier QB. Chiefs and Bengals have made the playoffs several times but struggled to make it to the superbowl. Is it because Alex Smith and Andy Dalton aren't top tier?
Joe Flacco won a superbowl a few years ago, I understand he isn't top tier but in the playoffs, he has played like a top tier QB same with Eli Manning. So my point is, relying solely on building a great team around a average starting QB is going to be much more difficult to sustain success over a period of time.
So I feel like you contradict yourself a little when you say " you don't want to settle and want to win a superbowl" - and just because we want to upgrade the QB position doesn't mean we wont continue to build a great team. Having a top notch QB just increases our chances of winning a superbowl.