That's neither here, nor there.

This is not about being able to find this or that niche musician that's great or even greater than any in the past, but about what the masses listen getting worse.

Music isn't just a solitary experience, but also a part of general culture.

As streamed music is getting cruder over time, the majority of the people are listening to increasingly shitty songs. That's chilling, regardless of whether someone can find 10000s of niche bands to listen themselves.

It's reductive to suggest that the top 100 represents "general culture" (whatever that ambiguous term means). There aren't solely niche musicians outside of the top 100. Theres plenty of musicians with millions of listens/views on streaming media that don't enter billboard lists that have extremely prodigious careers that have complex lyrics, use a wide assortment of instruments/equipments, evolve genres, etc.

Your data might be objective, but it's still a narrow slice of a much broader ecosystem.