I'm sorry but using that stretch with Rush as a basis to say they don't need Dak is the most disingenuous, insane argument I've ever heard. Those wins were primarily due to the defense and Rush doing just enough to squeak by. Anyone making that argument either has an agenda or lacks a fundamental understanding of the game of football. Blindly citing that streak is like saying Dak is the second best QB in the league after blindly citing his big stats without further context.
Regarding the OP's question, I don't know if Dak would be the same Dak if he were on a different roster, so I think envisioning Dak on another team is apples to oranges with Cowboys Dak. There is something "in the water" in Dallas that seems to make good players fall apart at the biggest moments since 1996. When have we had a super star who hasn't had a down game at the biggest moment? There are very few people paid to discuss and analyze football for a living who don't think Dak is a legit top 5-10 starter in this league, with some even putting him higher. That said, I think it would be like us getting Lamar, 2019 Stafford, or maybe Herbert at $60m per year. If we had been in QB purgatory I'm sure most of this board would be elated to be relevant again, despite the price tag. If we had Howie Roseman as a GM we'd be elated because we would know that paying a QB $60m per year still wouldn't keep us from fielding a team that could make a run. But we don't. We're stuck with a GM who will use that as an excuse to not spend any more money. It's sad, but it is where we are.
Do people really have Prescott as a top 5 QB or possibly higher?
I think he's a borderline top 10 QB and that's only because the depth of quality isn't what it used to be.
Generally considered to be the three elite quarterbacks with Mahomes comfortably the best:
Mahomes
Allen
Burrow
Jackson - multiple MVP with playoff issues needing to be addressed.
Herbert - he has put the team on his back but really been held back by a poor o-line, awful head coach, leaky defense and playing in a hard division.
Rodgers - multiple MVP and future first ballot Hall of Famer in twilight of his career.
Hurts - played exceptionally well in a Superbowl. MVP fav two seasons back until an injury very late in the season.
Stroud - looked smart in his rookie season and one to follow.
Stafford - Superbowl winner. Consistently good/very good for mostly bad Lions teams.
Love - looked more impressive as the season wore on. Regardless of the defenses, he played far better than Prescott in the play offs last season.
Goff - Played in a Superbowl. Better quarterback in the post season than Prescott to date. Coming off an excellent season.
Rodgers could be washed and Stafford does seem to be picking up more injuries but either way would the majority of NFL Executives take Prescott over the above quarterbacks given his horrific play off record on a good team?