I still think you’re wrong. For starters, the ones that take the possessive are not necessarily “physical entities”. We’re not usually referring the physical, printed, copies when we refer to poems, novels, symphonies, etc., we’re referring to mental constructs. Our ability to refer to Shakespeare as “the sonnets’ author” is not dependent on the the sonnets as “physical entities”. Also, we can use the same possessive construction to refer to hypothetical works that don’t belong to any identified writer, as long as they are specific (one might say “particularized") works. E.g.: “A novel’s author ought to be consulted before a movie is made from his story.”
Also, I would consider “feature(s)” in “feature(s) writer” an attributive noun, like “novel” in “novel writer” or “poetry” in “poetry editor”. The fact that these are being used to refer to categories rather than specific work is, I think, the key, but your previous explanation about “of” phrases doesn’t really cut the mustard as an explanation of what’s going on here. I notice that you don’t address my point above that one can make essentially identical “of” constructions out of phrases that use the possessive and those that can’t.
Specifically, I don’t think that this:
in this case you’re confusing two different senses of “of.” One sense is the possessive and the other is the object of action. In this case, the “writer” does not belong to the feature(s), therefore the possessive should not be used.
comes anywhere near explaining why “the writer of a novel” can be expressed as “a novel’s writer” but “a writer of features” cannot be expressed as “a features’ writer”. Again, I agree with the conclusion, but the explanation you gave does not explain.