Literature professor: Critics charge that the work of C. F. Providence's best-known follower, S. N. Sauk, lacks aesthetic merit because it employs Providence's own uniquely potent system of symbolic motifs in the service of a political ideal that Providence—and, significantly, some of these critics as well—would reject.
Conclusion
The critics argument should be rejected (it's not legit to say that Sauk lacks aesthetic merit just because he stole his hero's style and used it for a political purpose his hero would reject).
Evidence
Sure, Sauk stole the style from his mentor and the mentor wouldn't approve of Sauk's politics, but no one has shown that his writings are any less subtle or powerfully crafted than those of his mentor.
Evaluate
The author is rebutting a position by conceding the points made in support of that position (yes, stole style and had potentially objectionable political views) but arguing that they're not sufficient to prove the conclusion because something crucial is missing.
In this case, the something-crucial is that the people claiming Sauk's writings don't have aesthetic merit haven't really delved into analysis of the writings themselves. They seem caught up in tangential concerns, whereas this author thinks we should evaluate the material itself.
Goal
This question stem already has the Conclusion part baked into the question stem. It's cueing us up with "on the grounds that", which always indicates we're referring to the evidence.
So we need the best match we can find for, .