He ruined German music, according to Terry Teachout’s review of Forbidden Music: The Jewish Composers Banned by the Nazis:
The extent to which Hitler and his cultural commissars sought to control and shape European musical life has been chronicled in detail. But most of these books have dealt primarily or exclusively with German-speaking performers and those performing artists from other countries, France in particular, who collaborated with the Nazis. Yet the unswerving determination of the Nazis to rid Europe of what they called entartete musik (degenerate music) may well have had an even more far-reaching effect on postwar European musical culture. After all, many well-known Jewish classical performers—Fritz Kreisler, Artur Schnabel and Bruno Walter among them—managed to emigrate to America and other countries where they continued their careers without significant interruption. Not so the Jewish composers whose music was banned by the Nazis. Some of them were killed in the Holocaust, and none of those who survived succeeded in fully reconstituting their professional lives after the war.
One of the reasons why? It turns out the Fürhrer was a devotee of Wagner, in more than one sense of the word:
It is in no way surprising that Hitler should have paid close attention to Germany’s musical establishment, since he was an aesthete manqué with a passion for classical music. His ideas, moreover, about music and musicians had been shaped by Richard Wagner. “Whoever wants to understand National Socialist Germany must know Wagner,” he declared. Hitler read Wagner’s writings closely and took them seriously, declaring Wagner to be his favorite “political” writer and describing him as one of “the great reformers” in Mein Kampf. “Beside Frederick the Great we have such men as Martin Luther and Richard Wagner.”
Wagner’s pathological anti-Semitism was the insane root of the Third Reich’s suppression of Jewish composers. But one of the most striking aspects of this policy was the fact that even though Hitler promulgated a staunchly anti-modernist doctrine, it was not absolute in practice. Except for Hitler himself, Nazi leaders were comparatively indifferent to whether a given composer was a traditionalist or a modernist, so long as he played ball with them. What mattered to them—and to Hitler—was blood. If you were Jewish, it was irrelevant whether you were assimilated or observant, much less whether you were an atonal modernist or a Brahmsian conservative: Either way, you threatened the racial purity of German culture.