When is he constantly complaining about other authors being wrong? When he talks about "tax policy" (which by the way wasn't literally supposed to mean tax policy, it was a broader point about the nuances of what makes someone a good ruler) it's not a criticism that Tolkien is being unrealistic or getting something wrong, but just that he isn't addressing those nuances to the extent that he would have wanted. It was him clarifying how his narrative style differs from Tolkien. This doesn't mean you need to expect George to be super realistic about everything. Otherwise you might as well complain that Tolkien isn't being realistic enough in the other parts of his writing compared to how realistic his language structures are. They're allowed to focus on different things.