Great question. The question stem is asking us for the main point of the passage.
You asked why (E) is wrong. (E) is a true statement (according to the author's views), but the problem with (E) is that it's far too narrowly focused on the final paragraph of the passage. If the entire passage were just the last paragraph, then (E) would make sense. However, (E) fails to capture the author's main point.
What was the author ultimately working toward in writing this piece? Our first clue is in line 5, where the author states that "most historians" are doing something. This provides a strong signal that the author is likely to be resisting the fact that most historians continue to equate the term "woman medical practitioner" with "midwife."
The author's opinion of the historians equating "woman medical practitioner" with "midwife" is revealed in line 9, when she says that "this common practice obscures." We know she doesn't like this.
We're then told in the transition in the beginning of the second paragraph that the author thinks that although the stuff she has gripes with in the first paragraph helps somewhat fix the problem, she thinks that we must ask whether there exists an even larger problem going on. In the opening phrase of the second paragraph, "preserving terminological distinctions" refers to not putting together all women medical practitioners as midwives.
The deeper problem the author is suggesting there is in the second paragraph is why evidence for women medical practitioners comprises such a tiny fraction of the evidence historians of medieval medicine usually present.
Later on in the passage in lines 26 through 28, we're given some insight into a potential answer when the author asks, "Is this due to the limitations of the historical record, as has been claimed, or does it also result from the methods historians use?" The suggests the author has an issue with the methods historians are using.
Later on in line 35, the author says, "Nonetheless, the parameters researchers choose when they define their investigations may contribute to the problem." This shows the author has issues with their methods.
The third paragraph opens with the author's support of a chain in the historian's/researcher's method when she says, "The advantages of broadening the scope of such studies is immediately apparent..."
The final paragraph shows the author supports another change when she says in line 60, "Future studies might also make profitable use of analyses developed in other areas of women's history..."
From all of this, we know that the author's main point is to provide suggestions for ways in which historians can develop a more complete picture of medieval women medical practitioners.
(B) provides us with an excellent paraphrase of what we've identified as the author's main point, as it discusses how the quality and quantity of the information historians uncover concerning women's medical practice in medieval Europe would be improved if they changed their methods of study. This is our correct answer choice.
Does this make sense? It sounds like you forgot to keep in mind that in main point questions, we need to pick an answer that discusses the OVERALL point of the whole passage, not just the point of one of the paragraphs.
