Schenker was a music critic/journalist of his day who routinely used exaggerated rhetoric to inflate his claims towards his largely non-professional audience. The basics of his analysis method are genuinely remarkably well-founded in historical practice (far more so than the "harmony" practice that's taught in music-theory introductory courses nowadays), but they are also much better described and contextualized by fully considering historical sources, as opposed to a narrow focus on Schenker himself. For instance, melodic reduction (undoing diminution and teasing out long-range prolongational relations) was integral already to the Italian Solfeggio of the 18th century, as recently discovered by music scholar Nicholas Baragwanath https://global.oup.com/academic/product/the-solfeggio-tradit... . Schenker is getting a lot of bad rhetoric thrown at him these days, but he started that game in the first place.