> We can say: "A noun functions as a modifier. An adjective functions as a modifier." But not: "A noun used as an adjective."
https://www.grammar-quizzes.com/adj_nounmodifiers.html
https://www.merriam-webster.com/words-at-play/nouns-that-loo...
https://en.wikipedia.org/wiki/Noun_adjunct
The fact that everyone knows what a "layman writing style" means that the only place it's failing is your personal list of acceptable attributive nouns. But English isn't static. It runs on consensus. And consensus here that there's nothing weird about that use.
> while others' poor experience is a result of their more layman writing style.
would receive a low score: "Layman" is not a noun commonly used as an adjective where common is relative to the overall usage of "layman".
The adjective is "lay".
And, fine, let's call it an attributive noun rather than a noun used as an adjective. I was taught the noun as adjective thing in high school but happy to update my terminology. Indeed "layman" is not on my list of acceptable attributive nouns.
Did you notice how your first link says it's "incorrect" to use Kyoto as an attributive noun?
Hard lines rarely happen in the real world. It's best to be flexible such that you can accept unfamiliar instances of familiar patterns without trouble.
I happen to agree with you and disagree with the source -- "Kyoto man" is perfectly fine in my opinion.