Sentence Correction (SC) | Re: J.S. Bach was more prolific in terms of sheer hours of music composed

IMO, the reason why "including" could refer to "hours of music," an antecedent which is neither the subject of the preceding clause nor the preceding clause itself, is that "including" is not the start of a participial phrase, but of a adjectival phrase. The adjective "including over 200 cantatas" modifies the noun "hours of music."

Look at theseexamples:

"The police arrested at least 135 people,claiming that such detentions are for