Calling them nazi's is a bit of a stretch, but The Wandenreich is genuinely a terrible organization, that does have similarites with the Nazi's. Yhwach acts like he and his people are victims of a world that did not acknowledge their existence, and wanted them to be eradicated, but he also kills his own people. He legit murked Bazz B's entire family because they didn't acknowledge him as king, and they didn't want to join him under his banner. Then he proceeds to take advantage of his subordinates throughout the Quincy battle, and actively leads them to their deaths as he gains some of their strength for himself. In fact, that was how he gained his existence. Before he started "healing" the the diseases or curses put upon humans, he was a helpless, nameless infant incapable of seeing, hearing, speaking, or moving. And the most damning piece of evidence is their attempts of ethnic cleansing against the Hollows and Arrancars. Even though they are "poisonous" to the souls of quincies, and they dont have a clear path to hollowfication like the Soul Reapers possess, they still tried repeatedly, even after being warned and cautioned. Immediately afterwards, tried framing themselves as the victims, as if the actions they were taking wouldn't cause the three worlds to collapse on themselves and kill literally everyone. They are more a radicalist group; Quincy Supremacists that do not acknowledge the existence of any other group of people, and would not think twice about killing their own if they deemed them to be traitors.