I don't see that much of a problem. For a lot of music, limited variety in some important parameters is exactly what you want. Religious chants have virtually no timbral variety or changes of tempo and dynamics - the idea is you pay attention to the words. Electronic dance music and Moldavian folkdance tunes have very little variation in tempo, rhythm or tonality - the idea is you keep dancing for a very long time with a rather limited repertoire of moves and trance out. So for these genres, evolving to eliminate distracting complexity is progress. It's not like anybody would only listen to those anyway. (Exception: I have met people who said the only music they ever wanted to hear was Orthodox chant. They weren't folks I'd want to spend much time near).

I have absolutely zero nostalgia for the pop music I heard when I was a teen - thought it was either stodgily unvaried (like the Rolling Stones) or created variety only by tweeness (the Beatles) - and it seems just bizarre to hear people my age trying to recreate that stuff in singarounds, with all of what textural interest the music did have flattened out by reducing it to one man and a guitar. You'd hear more textural and rhythmic variation in a five-minute chunk of Mahler's Fourth than in the entire recorded output of Lennon and McCartney.

There was one odd feature of the pop music of the 60s and 70s which might confuse some of these algorithmic metrics. They often had a brief prelude where imagination was allowed to cut loose. I often looked forward to that bit and then tuned out completely once the 4/4 dance beat kicked in. Omit those intros from the analysis and there wouldn't be anywhere near as much difference between then and now.