For me, the sense in which it "unites a lot of seemingly disparate phenomena" is not that different than the sense in which "purple" unites a lot of purple things. It is true that they are all purple, but ultimately not very interesting or useful. Of course as a concept it is more complex and richer than "purple" hence why academics are able to write so many books and articles using it. I just don't recall ever having read anything that used these concepts to describe phenomena X and then felt like I better understood phenomena X, other than that I know realized it was sort of rhizomey.