Complex sentence: Nor is there any significant sense in which one composer was "schooled" by another (in the way that Berg and Webern were taught by Schoenberg), though it is true that Beethoven for a time received lessons from Haydn.
Split into simpler sentences: Nor is there any evidence that one composer was "schooled" by another, in the way that Berg and Webern were taught by Schoenberg. Although it is true that Beethoven for a time received lessons from Haydn.