We can't really say he's objectively a bad composer if there are people who appreciate his music, (regardless how many there are). "Classical music" is only regularly appreciated by about less than 1% of the total population. That doesn't make it bad music. The same logic applies to "avant-garde music".
But I still doubt how much of his musical philosophy overlaps with that of "classical music". I don't think general "avant-garde music" is "classical music". But, I would not say it's objectively worse than "classical music" in terms of artistic value. I know there are people who are into "modern art philosophy" stuff, I respect their preference.
'If you listen to Mozart and Beethoven, it's always the same,' he claimed. 'But if you listen to the traffic here on Sixth Avenue, it's always different.'
https://www.gramophone.co.uk/features/article/john-cage-manhattan-music
There are tons of genres out there that claim to be true descendants of "classical music". I just don't think it's fair to exclude them, yet include stuff like Cage within the boundaries of "classical music".
"Yuhki Kuramoto is a Japanese pianist and composer.
https://en.wikipedia.org/wiki/Yuhki_Kuramoto
At school, he studied Rachmaninoff and performed as a part-time soloist in orchestras.
Kuramoto's style of music shows influence from a variety of composers from different periods. Most notably, by Rachmaninoff, Chopin and Ravel.
https://www.famousbirthdays.com/people/yuhki-kuramoto.html
He was considered an heir to Rachmaninoff and Chopin."