I am not sure how one gets that far into an analysis of RPGs, J or otherwise, without even once mentioning characters, stories or themes.
Those games have never really been about mechanics to me. Sure, since they’re usually so long, they’d better try to keep things entertaining enough, but there’s a lot more to them (good ones, anyway).
I honestly don’t care much about the J, and even “RPG” seems so broad to me, because many, many games have blurred the line. Starting around end of the 90s when “RPG elements” became a thing. I don’t think it matters much.