Notice that the actual scientific article [1] doesn't make any considerations about quality.
It only takes objective measures and observes that they've been following the same patterns (probability distributions) over the last 50 years, just with variations on the distributions' parameters. Furthermore, they observe that the parameter changes over time are always to lower-variance versions for these distributions.
Finally, they argue that you could take a generic pop song from 50 years ago, modify it according to the current changes in parameters (adjust the harmonic progressions to the currently fashionable ones, change the instrumentation, and increase the average loudness) and it should sound like a modern generic pop song.
More importantly, they make no claims whatsoever regarding the quality of individual songs. In fact, they never study nor reflect on individual songs.
The original article's TLDR is: Music from the last 50-60 years has been using the same basic principles, and variance in timbre, pitch and loudness is decreasing over time between the mass of pop songs.
It only takes objective measures and observes that they've been following the same patterns (probability distributions) over the last 50 years, just with variations on the distributions' parameters. Furthermore, they observe that the parameter changes over time are always to lower-variance versions for these distributions.
Finally, they argue that you could take a generic pop song from 50 years ago, modify it according to the current changes in parameters (adjust the harmonic progressions to the currently fashionable ones, change the instrumentation, and increase the average loudness) and it should sound like a modern generic pop song.
More importantly, they make no claims whatsoever regarding the quality of individual songs. In fact, they never study nor reflect on individual songs.
The original article's TLDR is: Music from the last 50-60 years has been using the same basic principles, and variance in timbre, pitch and loudness is decreasing over time between the mass of pop songs.
[1] https://www.nature.com/articles/srep00521