Hi Chris, thank you for your question!
Overall, good job with your analysis! This passage requires a fair bit of labor in terms of tracking the three viewpoints you mentioned, but I'm glad you were able to sort them out. For a deeper dive into your interpretation, it may be useful to go viewpoint by viewpoint, so let's start with Rewald!
Your interpretation of Rewald's viewpoint was great! It really summarized the information we know about Rewald focusing on the stylistic elements (or the "how") of Impressionists as well as Rewald's status in the historian community.
In terms of Herbert, your overall analysis is basically spot on! Herbert turned away from Rewald and emphasized the "sociocultural context" of the Impressionists, focusing on the subject matter (or the "what") of the painting and the social issues that arise from the subject matter (exemplified by unequal treatment of people and the exclusion of modern industry).
Regarding the author's viewpoint, you made a great use of how the author's tone/word choice really showed they have some issues with Herbert. Ultimately, I think you ended in the right place with the author (that they believe focusing only on style like Rewald or only on subject matter like Herbert is bad), but let's discuss some of the part where you mentioned getting a bit lost!
Starting at the beginning of the third paragraph, we're faced with another reason why the author has an issue with some of Herbert's rationale: Herbert undermines his own rationale because of his own concession that Impressionists were not particularly conscientious. The author then uses this point regarding how they leave out ordinary experience and then transform whatever they do actually paint by a style that is only indirectly related to the subject matter they depict (lines 51-55). The author proceeds to then assert that Impressionist paintings have two layers - the "what" and the "how" - and to emphasize one without the other is bad!
I hope this helps and I imagine you will find that your interpretation lines up with many of the correct answer choices!!
Kate