Would you pay Brock Purdy $55 million a year to be Saints franchise QB? [mod edit]

Geldo's right on. Strictly, prime Peyton Manning and Tim Brady were system quarterbacks to the extent that when they moved on to different teams, their offenses went with them. Manning in Denver and Brady in Tampa, respectively, were their teams' de facto offensive coordinators (for Brady, after a few games wrangling with Bruce Arians).

If you put either of those guys, in their primes, on the Dennis Allen-Pete Carmichael 2022-23 Saints and forced them to run exactly the plays Carmichael called (no "Omaha" stuff at the line), they'd have looked only a little better than Derek Carr looked. Let them run Manning's "Tom Moore" offense and the stuff Brady & Josh McDaniels cooked up in New England, however, and even Dennis Allen's Saints would've been a contender for the NFC title.
I'd say don't fall into the trap of equalising all QBs based only on the offensive system as the true differentiator. That's an excuse someone has been trying to peddle around here for too long, for a serial failure at the position they can't quit their love for.

Being in the right system, the right coaching, the right culture, the right team around them are all major factors for QB performance, but the likes of Manning and Brady would still be head and shoulders (and chest and hips and more) above the likes of Carr, even if all other things were equal. The book on Carr has been out for a while, he needs a clean pocket, the opportunity to uncork his arm for deep shots and a soft handed intermediate target to bail him out, usually at TE. Those other guys you mention were far better, in adversity or otherwise, on a consistent level that Carr won't ever touch, being completely truthful. And I say that hoping he has success here, but the comparison with those HOF players is entirely unequal.