Maybe -- but the context to understand what Debussy and Ravel were doing (maybe not Scriabin) is to get the Bach / Haydn / Mozart / Beethoven / Schubert under your belt.
I agree! But it seems that the books all stop at 1850. Or they toss in a few cursory chapters at the end. (If there's some text that doesn't do this, I'd love to read it.)
I've looked at that book before, and while I agree that it's probably worth reading it sure doesn't answer all the questions. It just talks about voice leading and gives scientific explanations for why the 18th century rules of part writing reliably turn out pleasing music. It doesn't account for all the music that satisfies listeners somehow even while violating some of those conventions. Nor does it cover anything aside from tonality, from what I remember.
But yeah, the development of tonality kinda stopped in the 1850 range, with maybe Stravinsky, Tatum, and the 1940s Bebopers extending it as an exception. But at that point, tonality had passed out of the "art world" -- everything post-Duchamp's "Fountain" has been a bit more deconstructive and nihilistic.
Maybe of note, pun intended, Schoenberg was pursuing the "emancipation of the dissonances" while the Bolsheviks were destroying Russia. And of course, that's part of why nobody listens to Schoenberg or performs his stuff -- it's grating and kinda horrible, at least after he abandoned high Romanticism after Opus 5.