To me this is a very common misinterpretation of the state of music. Out of context. The study is about "Top 5 Billboard" Songs. If you think the Top 5 is representative for music in general... well than you only know the Top 5 Songs of each year. Listening to only 50s pop music for example can feel simplier and dumber to me ... most of it is in the blues/country/folk context ... too many of them with simple lyrics about disgusting older men trying to convince very young women to have sex with them. But this is another topic. In the 21st century pop music you can easily find so much more variation. You can find good blues/country/folk stuff, too. But think about all the other styles like electronic, metal, hip hop which vary in their own ways. In this context, music is getting more complex and I would do myself no favour, ignoring them, being that Rick Beato kind of "everything was better, now everything sucks" ... @soundog: this rant is not about you in personal I respect your opinion.
(I only looked at pretty pictures) Broadly speaking, the faster the song, the less complex it has to be in every other aspect. Metal covers the entire range, from highly complex but fairly slow to 260 bpm subgenres using no notes and no rhythmic variation. If faster music is pushed by the industry, then simpler music is what we'll get.
