One sense of "advance" does mean to improve, but another commonly used sense is simply to "move forwards". History advances, literature advances, music genres and technique advance, time advances. None of those imply improvement or a value judgment, just moving-forwards and building-upon (or building-in-reaction-to).
You can absolutely say drama has advanced since Shakespeare, and few people would misunderstand. To say it hadn't would mean nobody had continued to write plays in the same tradition of western literature.
(See [1] and contrast definitions 2 and 3.)
> To say it hadn't would mean nobody had continued to write plays in the same tradition of western literature.
To say it hadn't, in my sense, would mean nobody has written any "better" music than Beethoven's 9th. Nobody has.
To say it hadn't, in your sense, would mean the form of the symphony hadn't continued to evolve, and of course you're right that it has.
All i've heard is mostly the same types of "sound" copied over and over again. Nothing jaw dropping so far (but there is definitely something that has to come out of this technological revolution one day...)
Doesn't mean anyone will be watching that dog video in 50 years.
What I will say is, arts do not advance linearly, more or less, like science does. You can't say that drama has "advanced" since Shakespeare -- it's just changed. So "what's popular?" is not a shorthand for "what's good?"