You've probably both heard and invented it; it's one horn of what we might call the Progressive's Trilemma: "If traditional structures are not optimal, they must be either a) insufficiently optimized, b) optimized for the wrong values, or c) optimized for the wrong conditions". I doubt you'll find many progressives who don't believe some measure of each of these depending on the issue.

(EDIT: You could call it the Chesterton's Fence trilemma: If the fence shouldn't be there, then either it was put there by an idiot, it was put there by a bandit, or it was put there when the road ahead was flooded. Or something.)

a) is my point above and b) is related to OP's Normative Assumption #1. c) is a bit related to OP's Descriptive Assumption #3, but might warrant its own statement: There has been so much rapid change recently that something working in the premodern past is scant evidence that it will work today (prod) vs. the lessons of the past mostly hold true today (NR).

This one is fun because it lets you say "<Historical figure> was indeed wise to counsel thus, but <Neoreactionary> is a fool to apply that advice today". Perhaps ironically, this has a cultural-relativist-ish appeal to progressives.

(But having a motivation doesn't make it a bad argument)