How to Tell If a Programmer Is Competent or Not
medium.com
medium.com
They propose a number of personal beliefs about what constitutes competency, whereas I will contend that there is no "silver bullet" by which a non-programmer (or XYZ profession) may assess the competency of the potential hire.
I could write a different article on programmers who seek to undermine existing code in order to get a green field project out of it. While I can completely comprehend what may lie behind a total rewrite (and have plowed through some rather thick ones) I would be wary of hiring such a rigidly ideological person who suggested "throwing it all away and doing it over" as this person is likely somewhat obtuse in their own way.
Human factors also matter.
Unsure how I am, as you say, "swinging bladed weapons around while blindfolded." Very colorful terminology, but I'm a little confused by what you mean.
The "silver bullet" term you're using I'm guessing is borrowed from Mythical Man Month, where Brooks suggests that no single advance in tech within a decade provides an order of magnitude improvement in productivity. I don't think that necessarily applies to helping non-technical people vet out programmers. I think I'm more giving these people a lamp in complete darkness.
I don't think brownfield projects created by great programmers are a bad thing. In fact, I've learned a lot working in brownfield projects. I do think though, a newbie programmer that, in a microcosm, creates a their own unique masterpiece loosely inspired by MVC, gets crushed by complexity and bugs, and then quits for supposed personal reasons, is a very real potential disaster for tech projects.