I only partially agree with the author here, in that I don't think that there are too many mediocre artists, in fact I think we could do well with more mediocre artists as well as more talented artists. However, I do think there are too many artists trying to make a career out of art, and that a shockingly large proportion of those artists are mediocre at best.
There's this really toxic idea in liberal ideology that the purpose of art should be to promote the correct emotions and improve social problems. From that, we get people who feel that they are doing the right thing by encouraging someone to make a career out of art who otherwise would not have due to not having talent. That's a shame, because that mediocre artist who will now live in poverty due to their poor career choice could have instead gone on to have a very rich and rewarding art hobby along with a less glamorous but more profitable career.
The issue is that there are definitely also too many extremely talented artists out there, as well as musicians, writers, actors, etc. Most very talented people are still unlikely to make enough money to live off of, so they either need the support of someone who has a "real" job, or they need to practice their art as a hobby rather than as a career. Since the former isn't an option for almost all people, if we want more talented artists, we should encourage and teach people that you don't need to make a career out of something just because you love doing it, and that there is value in things outside of how much profit you can make doing them.