Personally, I don't think having deep domain knowledge is as important. However, being able to write the spec based on interactions with the client / customer / stakeholders is. (The AI Math and hardware optimization "never" being doable by an AI seems like an arbitrary distinction to justify one's choices.)

Incidentally, I put the word "only" in quotes because I morally and aesthetically appreciate the strength of someone who can write to spec. I have no interest in demeaning the effort it takes to do so. I have worked with supposedly senior developers who ignore specs completely, even when the specs are done by a technical person and include details / unit tests.