the claims made in support of this conclusion have not been shown to be
Why this is right
Well, this is mainly through elimination that we'd like this. Since our author is saying "granting the truth of your supporting claims, it has yet to be shown that these facts say anything bad about Sauk's writing". Since the critics are concluding that Sauk's writing lacks aesthetic merit, the criticism should be focused on the artistry, or lack thereof, of the writing. This author doesn't explicitly say that "whose style you copped" or "what political views you were hoping to serve" is irrelevant to aesthetic merit, but we can plug in a little common sense and interpret the author's words that way. It's kind of like someone arguing that Michael Jackson's Thriller is not a good album, since Michael Jackson was a very complicated public figure who had scandalous allegations levied against him. Someone might say, "I'll grant you he might have done a lot stuff wrong and been a weird guy; but that has nothing to do with whether or not this album is a good art." One final clue we can use to make ourselves like this answer more is that the author actually rejects the conclusion. If we were nervous that it felt too strong to say this author thinks the critics' supporting claims are irrelevant to their conclusion, it might help to remind ourselves that the author's argument basically sounds like this: I'll grant the critics the truth of their two supporting claims, but they've yet to show X. So their argument should be rejected. If the author thought the two supporting claims were at all relevant, then the author's conclusion would have probably been more tentative / hedged, sounding like "you've only 60% convinced me; I still need to know X", rather than "this argument has 0% persuasiveness to it; it should be rejected."
Skill tested: Method · how this choice captures the argument's function is the move to repeat next time.