I'm sorry but this really betrays history, even contemporary history.
We could point to a number of contemporary artists that are worth millions of dollars for whatever they are known for - you might even consider them 'rockstars', regardless of how myopic I find the term - but headlines that make it onto the "4 big websites" is not the same thing as being irrelevant.
For every "Picasso" you can cherry-pick from history there's a Jeff Koons, Damien Hirst, Banksy, Ai Weiwei, etc - All worth millions or, at the very least, "Rockstars" in their own right.
The idea that Marble Sculptures in Ancient Rome or whatever had passersby standing in amazement compared to today is not accurate. People walking into whatever temple for whatever God they were visiting would be just as bored by the marble back then as you are of marble now.
What's really changed is that accessibility to these things have exploded. More people than ever have access to Art, Art Tools, Art Education, and new Art Mediums. "Art" is in no-way dying out. Focusing so much on the "Medium" is missing the forest for the trees, honestly. (Which is to say, modern technology and socio/economic trends have a bigger effect on the use of Marble than "Marble as a medium", whatever that means. Sculpture is alive and well, I promise you)
This is a little bit rambly because your post just kinda says, "Art changes over time" and doesn't, in my view, have a wide-enough vision of the "why" but this is all to say that like, as far as this thread is concerned, Visual Art, if anything, is omnipresent in our lives - not less relevant than in times past. If anything, the presence of "Rock Stars" is an indication of too few talented people, instead of what we have historically which is an ever increasing number of extremely talented people. I just don't know how we can say Painting is less relevant now when more people than ever are doing it lol.