It's highly possible that the most underrated composer in the history of music is still Joseph Haydn. There are literally thousands of underrated composers out there and probably only a dozen or a dozen and a half who are genuinely overrated, but at least in my opinion, the founder of modern music is Haydn, not Bach.
I've written at least three or four long blogpost essays nobody reads about how Bach's place in music is overvalued, and I really don't want to write a fifth, but there is something about Bach that, to me, is too heavenly, too divorced from the human experience, too, as we Jews say, 'goyish.' When you get to know Mozart and Beethoven's music, they take on the quality of old friends, but when you get to know Bach, both the glory and the weakness of it is that it never stops being an extraordinary experience. The music is too perfect. There's expression aplenty in Bach, but it's not human expression, it's the expression of divine beings. These divine beings might feel compassion for our suffering, but they can't relate to it, and they rarely ever seem to relieve it. Furthermore, where's the humor in Bach? And most importantly, where's the fallibility? You can search far and wide for a compositional weakness in Bach, and you might find one every million measures. That, as far as I'm concerned, is the ultimate compositional weakness. It's like music assembled by a kind of celestial computer coding. He was so masterful at counterpoint that through his counterpoint he practically created the common harmonic language we use to this day.
But this was entirely an accident. Very few composers knew more than a few pieces by Bach until Mendelssohn worked mightily to revive him in the 1830s to a fame Bach never had in his lifetime, and performed Bach with a seraphic beauty which was antithetical to instruments and performing style of Bach's period. The Bach of the Romantic era was a completely different composer, grounded in harmony rather than counterpoint. As a personal interjection, when I hear Bach performed on original instruments, rendered little different from a generically excellent composer of the Baroque period, I begin to understand why Bach's employers in Leipzig offered Bach's job to Telemann or Graupner.
Bach's music is pure counterpoint and harmony, there is no flash, there is not even really a style of which one can speak. There is only pure substance; as the musicologist Jan Swafford put it, nobody ever wrote better notes than Bach. In the same way that Immanuel Kant is often considered pure analysis and thought and system that gives little consideration to stylistic clarity or common wisdom for layman readers, the vast, vast majority of Bach's is a pure contrapuntal and harmonic thought that gives little thought to instrumental color or rhythm. Both were revolutions for the humanities that gave them something like the rigor of science and for this pseudo-intellectual, both revolutions achieved more rewarding results when their successors turned their soft science back into art.
Now that this era liberal democracy is in danger of ending, Bach calls to us like a siren song across the authoritarian sea from a place and time when submission to despotism was absolute. Surrender your critical judgement, it seems to say, and you will be happy.
Clearly I'm missing something, because so many millions of people are on intimate terms with Bach.