"The band released several unheralded albums in the '70s but never reached the height of 1969 again"
That's a questionable take– "There's a Riot Goin On" (1971) and Fresh (1973) are both absolute classics and highly influential
The Swedish, rather short-lived but very influential, magazine Pop voted There's a Riot as the best album of all time in 1994. That list had a huge effect on a whole generation of Swedish music fans.
https://sv.wikipedia.org/wiki/Tidningen_Pops_lista_%C3%B6ver...
Never dug much into sly stone, only knew 'you caught me smiling' from this album, it's indeed an very interesting one.