IMHO Moondance can just about be classed as jazz, it’s just played very badly. And, of course, when something gets played to death it ceases to be called jazz (emoji denoting heavy irony).
When I was a young buck we had the same argument concerning the classification of a sports car. It started with cars with open tops. Then the Lotus Cortina came along and confused everything.
I suspect the jazz definition was dead easy in the 1920s when there was no other form of ‘lively music’ to compete.
I did a jazz trio gig the other day and amongst some Monk and Miles we played a version of Sukiyaki, a pop tune from the sixties. So, go figure.