I think he says a lot of subjective things like they are objective, he says things to fit a narrative(''Mozart fell out of favour and commissions began to go to more compliant composers'' biographers attribute Mozart's late financial woes mainly to his spending, his music was highly acclaimed by connoisseurs and among elites. Using this to paint Mozart as someone rebelling against elitism is really weird when you consider that Mozart was a Freemason.), and a lot of his beliefs sink in water without truth to hold to. His authoritative tone on top of it is probably why people get annoyed by him.