Your comments re: "There's A Riot Goin' On" confirm what I've said all along
specifically when you had similar revelations about Stevie Wonder and Funkadelic: since most of your favorite music is complexly melodic, it's probably going to take you longer to appreciate more groove-based soul music on its own terms. But I'm glad you aren't giving up and are eventually seeing the light- better late than never. Maybe now it's time to revisit Sly's other 70's albums? Aside from "Fresh" (which seems to rightly be regarded as almost as good as "Riot"), those albums are ridiculously underrated IMO.
Similarly, I hope your love of Mingus eventually leads you to appreciate more jazz artists. Will also probably take some timer but I have faith.