There are so many levels of “good.”
Yes, non Jews can be incredibly talented and compose music that is enchanting and delightful. But they can also cook pork and shrimp that are exquisitely flavorful.
“Good” is a definition that one must define within a Jewish lens.
Good is not solely a level of enjoyment; it is something that is beneficial for our neshamos.
Good can be painful at times, like a bitter medication that a child must take to combat dreaded illness. Good is not always fun, but it is what we need, even if we don’t like it.
So “good” music, in Jewish terms, is music that arrouses the neshama in closeness to Hashem, that causes one to do teshuvah.
There is enjoyable music b’goyim, but usually not really GOOD music.
(The exception to the rule is jewishly “good” music that came down through the rare non-Jew, like the Russian marches that were adopted by Chasidim. Sometimes, sparks of holiness are able to be accessed by talented composers, but only a truly Holy person will be able to tell you which songs fall into that criteria.)