Did the Nazis truly hate Mahler? He had his finger on the pulse of everything that the Nazi worldview dealt with, and his music is nothing if not romantic, something the Nazis loved. He even converted away from Judaism and married out of the culture. The 9th symphony is a tragic reflection on the destruction that modernity would bring to the world. I think if the Nazis didn't know of his ethnicity they would've held him as the peak of music. Why would they condemn such art as degenerate??It doesn't make sense, even with their hatred of Judaism.
They also hated Mendelssohn only because Wagner was assblasted at him just for existing