I'm not qualified to make judgments about Jazz, but, as they say, I know what I like! I dig the late big bands of Count Basie and Duke Ellington, who wrote great compositions and arrangements, and had superior musicians. One such was the incredible guitarist Charlie Christian. These bands also swung like crazy! I also like the small bands, songs, and singing of guys like Mose Allison.
One genre related to Jazz that is consistently overlooked is that of Jump Blues, which I love. Louis Jordan is the best known practitioner of the music, which was basically a Blues "shouter" fronting a small jazz combo consisting of a pianist, upright bassist, drummer, a couple of sax players, and a rhythm guitarist. It was with Jump Blues mixed with Hillbilly that Elvis and the other Southern whites created Rockabilly, the original, pure form of Rock 'n' Roll. Rockabilly bands didn't have a drummer---it was the job of the singer/acoustic rhythm guitarist to emphasize the 2/4 backbeat with his strumming. That's how Bluegrass bands work, too.
I'm of an age to have been in the target audience, in my perception, of the direction Miles Davis took in the late 60's. I didn't like that music then, and I don't like it now. The Fusion movement, grafting Jazz onto Rock, created, imo, a grotesque, hideous monster. Others disagree ;-). Speaking as a drummer to a drummer, I didn't like the style of playing of Billy Cobham then any more than I like that of Neil Peart now. Gratuitous displays of empty virtuosity leave me cold.