If (and that is a big if) using opponents results pleasing pairings only with some specially crafted wonky RYB colorspace then to me that is more just an indication that using opponents is not a robust way of picking pleasant pairings.

I am also very dubious about the claim of the color pairings being more or less "culturally relevant".

They're more pleasing because artists and graphic designers used RYB pairings for decades, these pairings all over the place in analog and digital media, people are more used to them. Even Adobe still uses an RYB wheel in their software, RGB only for color grading (it still deviates slightly from a normal RGB color distribution).

RYB is more culturally relevant because artists and designers "produce" culture based on it.

> Classic colors of royalty

I think this is a stretch, red and blue are also classic colours of royalty.

Purple was the color of royalty because it was expensive. Same for gold.