This may be a long-winded response, but I thought I would read the passage and offer you my realtime thinking BEFORE I've read your passage summary and BEFORE I've looked at any answer choices.
Here's what I was thinking about as I read the passage (if you're familiar with Manhattan LSAT's P.E.A.R. process, this is essentially what I'm recounting to you):
1st line makes it clear that the topic of this passage is a book. Generally, when a passage is about a book, there are three options for the purpose/main point:
1. To summarize the main points of the book (fairly neutral tone - main point would be the best overarching or noteworthy idea the book's author wants to communicate)
2. To criticize some aspect of the book (opinionated tone - normally the author of the passage agrees with much of what the book's author did/said but points out that the book's author failed to consider something important)
3. To clarify a misconception critics have of the book (opinionated tone - normally we get to hear what critics have typically said about this book before the author of the passage swings in with a but/yet/however towards the end and 'sets the record straight')
So as soon as the 1st sentence is done, I start wondering which of these paths we're going down.
It's hard to tell by the end of the 1st paragraph, but so far it's just been doing #1, summarizing the book's key points. Several times in this passage, the author says that the book is "not doing ___ but ___". These are important distinctions that will likely appear in the questions.
So from P1, I get:
- we're discussing this book about communism in 1930's-ish Alabama
- book wants to focus on how African American workers could embrace communism and how communism could serve as an organizing force
P2 starts of with a "MOST scholarship has said ____", which is a classic LSAT setup for but/yet/however THIS guy says something different. Indeed, P2 seems to reiterate P1's point that this book is mainly concerned with how the communist party worked as an organizing force. The important line seems to be 20-21 ... the Popular Front was NOT good as an organizing force.
P3 explains that the preceding period of the communist party WAS a good organizing force (strong rhetoric appealed to sense of deliverance ... help from afar).
P4 returns to the idea that the Popular Front was NOT as good as an organizing force and led to a decline in African-American participation (more moderate tendencies weren't as conducive to what African Americans found appealing about the preceding period).
P5 is more of a summary/takeaway paragraph. The book does not completely BLAME the Popular Front, because other unrelated factors apparently also led to the declining African American participation during that time period.
Okay, so this was definitely a #1 ... the author just summarized the key points of the book. There's almost no opinion from the author, so we need to think about Main Point in terms of the main points of the book:
- Kelley cared about organizing potential of the communist party for African Americans
- Third Period was better at organizing/enthusing African Americans than Popular Front was (although other factors contributed to the decline)
Those are the big ideas I would think would be in the correct answer choice, but let's see what we can get rid of:
(A) "fails to fully explicate" is the giveaway for me here. The author wasn't slamming the book. There was almost ZERO author opinion.
(B) "ideological purity" and "effecting political change" strike me as out of scope. These weren't among any of the big ideas I remember reading about.
(C) Maybe? "valuable tool" is pretty opinionated, and I don't know if I have support for that. I didn't think "models of unity between radicals and liberals" was a big idea, either. (If you research this line in P2, you see that this phrase was used to describe OTHER authors, not Kelley.)
(D) "true measure of success" seems loaded. Did we talk about "interacting with their culture"? Is that the same as "serving as an organizing force"? This answer choice doesn't even mention the book. Wasn't that the focus of the passage. This answer choice acts like the Communist Party is the main focus of the passage.
(E) "offers new insights" is a little loaded, but otherwise this is a generic way of talking about the fact that the Third Period was better at organizing/exciting African Americans than the Popular Front was. Can I find textual support for "offers new insights" so that I can confirm this? Kinda. The "most scholarship" detail from line 10 allows me to say that Kelley's is different. That seems to be the only supporting line for "new insights". Not perfect, but this seems way closer than the other ones so I'd go with it.
Okay ... now that I'm done with that unbiased recap, I just read your passage summary. Looks like you nailed it (I say, arrogantly, because we pretty much got the same thing out of it).
I agree that (E) is a weirdly worded answer, but a lot of RC is about accepting the answer that isn't technically wrong.
I think the answer choice and the Superprep explanation you cited are going overboard with saying "new insights" and "breaks new ground".
However, there's definitely textual support for the idea that Kelley's perspective was not like MOST scholarship. I think the fact that there were also three sentences in which the author said that Kelley was "not doing ____ but rather doing ___ " is also giving us reason to believe that the 1st half of those thoughts is the TYPICAL approach, making Kelley's 2nd half a more unique take on the subject.
I notice you haven't mentioned any other answer choice that you like more than (E).
Let your takeaway from this question be that we often have to get the credited response by being confident about eliminating the broken choices.
Let me know if you have lingering qualms/questions.