Actually, this issue comes up a fair bit in SCs, but I usually explain it a different way (what was said above wasn't wrong, but let me try tackling it from a different angle).
In everyday conversational English, people say things like
I love the cat more than the dog.
Common sense would tell you that the speaker means, "I love the cat and I love the dog, but I love the cat more" (common sense especially if you're a cat lover

). But grammatically, it'd be considered wrong on the GMAT. It's ambiguous. It *could* mean "I love the cat and the dog loves the cat, but I love the cat more than the dog does."
This kind of ambiguity in comparisons is considered wrong in formal written English, and it gets tested quite a bit on the GMAT. You fix it by adding an auxiliary verb and, if necessary, repeating the subject -- "I love the cat more than I do the dog" or "I love the cat more than the dog does."
In the example here, A *could* mean that the work of Charles Chesnutt reflects characteristic interests of his contemporary local colonists as much as "the intellectual ferment and historical reassessments, etc." reflect characteristic interests of his contemporary local colonists. E fixes that.