Players like Darnold are retread because of the scarcity of quality QBs. Now, he'll be paid like a franchise QB if he continues having the season he's having.
I don't think we really disagree on a lot of this. The "franchise" label certainly isn't what broadcasters make it out to be. I just believe it is applied because it is hard to find a QB you believe is capable to leading your team to a Super Bowl. Once you find one, you pay them because it might be a while before you find one again. You seem to think they are a dime a dozen, but the evidence doesn't bear that out.
Again, I'll use the 2021 Draft as an example. You had Lawrence, Wilson, Lance, Justin Fields and Mac Jones taken in the first round. Only Lawrence has proven worthy of a second contract. Kyle Trask, Kellen Mond and Davis Mills were taken in the second round. Trask has 11 pass attempts in his career so far. Mond has three. Mills was so good as a starter that the Texans used a first-round pick on C.J. Stroud.
That's 1 QB out of 8 that could be considered a quality starter/franchise QB. 1 of 8 equals scarcity. But maybe one of those other seven will experience a Mayfield/Darnold renaissance before their careers are over ... and get to be a franchise QB all over again.