I see Nietzsche's critique of Christianity highlighting its incipient nihilism: by imposing values it undermines the ability to find/ create one's own, so I don't see that as presupposing realism. — Janus
Nietzsche's critique of Christianity (specifically
The Antichrist) amounts to the charges that Christianity is both
false and
pernicious. Specifically, Nietzsche identifies and critiques what he believed to be the foundational presuppositions of Christianity: the existence of God, the existence of an afterlife or other world, the existence of a moral world order, and free will. He ultimately claims that these presuppositions are
false, and that the values they promote are internally inconsistent, and that their falsity/inconsistency makes them morally
wrong or harmful in some way.
This is all
highly realist, at least implicitly: critiquing a religion/its system of values on the grounds that their foundational truth-claims are
false and their values
morally bad/harmful (which, of course, seems to imply that there
is such a thing as truth/falsity, and some fact of the matter as to whether a given set of values is bad or harmful in some meaningful way).
And there are many other passages where Nietzsche says things about e.g. truth, perception, science, and so on that are also
highly amenable to realist/cognitivist interpretation (e.g. the beginning of
Human All-Too-Human where he talks about the "knowledge" and "truths" the historical sense has achieved, and contrasts that with the "error" and "mistakes" made by theology and metaphysics): He praises the sciences (especially in
Human All-Too-Human) and the senses (e.g.
Beyond G&E 134,
Twilight of the Idols III 1-2), and often waxes poetic about "knowledge" (e.g."With Knowledge, the body purifies itself; making experiments with knowledge it elevates itself; in the lover of knowledge all instincts become holy"-
Zarathustra) and "truth" (e.g. "How much truth does a spirit endure, how much truth does it dare? More and more that become for me the real measure of value... Zarathustra is more truthful than any other thinker.."-
Ecce Homo).
But then, on the other hand, there are many other passages where he seems to be advancing an
anti-realist critique of these things,
often in the same work (i.e. elsewhere in
Human All-Too-Human he says, "A man may stretch himself out ever so far with his knowledge; he may seem to himself ever so objective but eventually realizes nothing therefrom but his own biography", and elsewhere in
Beyond G&E he says "science at its best seeks most to keep us in this simplified thoroughly artificial suitably constructed and falsified world").
So this is a deep tension running through much of Nietzsche's philosophy (which keeps Nietzsche scholars endlessly arguing in circles) which is not possible (imo) to completely resolve or reconcile, because this was simply how Nietzsche's mind and method of philosophy worked (for better and for worse).
But so this is also just part of what makes Nietzsche so interesting (imo): he was (explicitly) opposed to philosophical systems, and his views are often very difficult to square with one another or to try to construct some coherent system out of. And sometimes he says things that are in tension with (at a minimum), or even outright contradict things he's said elsewhere. Much of the time he seems less concerned with what is true or self-consistent in some technical or straightforward sense, or amenable to some systematic treatment or analysis, and much more interested in some deeper penetrating insight about how some things work. Which he occasionally achieved, imo.
So Nietzsche wasn't
right much of the time, but he was
always interesting, and often deeply insightful. And so I agree completely with what you said about being concerned with whether a given philosopher is interesting or insightful as much if not more than whether they are right or correct or perfectly self-consistent, which is why Nietzsche is (and probably always will be) one of my personal favorite philosophers.