Thanks, I think I basically agree. I guess my complaint is that these later composers generally involve more "bespoke" analysis because of the additional complexity, which is not treated adequately in the textbooks. (Whereas, for example, for a lot of Mozart piano sonatas you can just write down all the roman numerals and call it day -- I'm joking but only slightly.)

Also, I think you'd call your Mozart example a common tone diminished chord, notated CT7. I think this is pretty standard nomenclature now; see this book excerpt for example: https://viva.pressbooks.pub/openmusictheory/chapter/common-t.... Especially the example under the section "recognizing CT7 while analyzing."