Ah, but "good" is an opinion, and not a provable assertion
You, as a scientist, know that I am sure. I for one don't think Gershwin's music is "good". I think it is tuneful and sometimes interesting and I like the piano renditions he did of some of his popular songs, but I don't think he is in the same class with Bix Beiderbecke, and I am sort of surprised no commentary from him seems to have been recorded regarding Bix's music. Whiteman seems to have seen Bix's value, since he gave the piano pieces a prominent place in some performances, even though they bore no resemblance at all to Gershwin, and it seems unlikely that they would have created the same type of sensation that Gershwin's orchestral music (at least Rhapsody in Blue) caused, with the fame, ticket sales, etc., even with the promotional boost Whiteman could offer.
The reason I like the Schoenberg quote is that he is giving a musician's opinion of another composer. Music so rarely benefits from a "word" interpretation, so it is interesting to hear this assessment. Without being an expert in any way, I'd go so far as to say that Schoenberg was indeed a musician, who, alas, was unable to write music. But it appears he had some interesting things to say about it. At least to me. I am grateful for the post.