Most popular art is forgotten. There were hundreds, if not thousands of plays performed at the Dionysia in Athens, but only a handful survived the test of time. And even fewer popular novels are remembered. (Yes, the ancient Greeks had a kind of novel.)
What this tells us is not that popular culture is constantly changing, much less progressing. What this tells us is that popular culture is basically not much good. It tries to hit the commercial sweet spot between challenging and overfamiliar. The cheaper productions costs for commercial (aka "popular") art of al kinds means a flood of more mediocrity. Older people who are more familiar with the tricks that commercial art uses tend to value it less. This appears to be the main cause of complaints that standards are lowering, but the increasing mass of mediocrity probably plays a role too. And inexperience tends to lead younger people to overvalue their first exposures.
Incidentally, the generation gap phenomenon is far more about resistance to changes in social mores, rather than directly about art of any kind. Conservatives are more into "kids are rotten" than "kids don't know good art." I don't think anyone here is even tacitly arguing this. I plan on ignoring any such suggestions myself.
The really interesting question is how we could know if standards were really changing. There was not too long ago an effort to objectively study the variety in pop music. As I recall it counted things like types of instruments, changes in key, length of phrases, etc. The results unambiguously indicated that the Sixties were the high point for variety, while the trend since has been for an ever decreasing variety, especially for the most popular songs.
And it is a matter of historical record that people like Ausonius conceived themselves to be artists on par with those of their past. Yes, it is possible for cultural standards to decline. Yes, it is possible for this to be passed off as mere change. No, it is not possible to deride the questioner as a scummy codger who has the temerity to talk as if he weren't innately worthless.
When I was a kid I didn't think I had a right to walk on somebody else's lawn. Reflect.