GCT - it is a common strategic ploy to assign some form of “ultimacy” to any view, when that view disagrees with an absolutist view. But it is illegitimate to do so. Materialism can be viewed as a form of epistemic “agnosticism”, if you like, as it may only be an appeal to “scientific” verification. This verification has as its origin an appeal, in turn, to linguistic analysis, which is the logical positivist perspective. My position, taken as a whole, however, contains no epistemology at all, per se. I simply do not ask the question “what is the ultimate nature of reality?” because my position is that this question is itself nonsensical. This is by no means a position original to me.
Put another way, I do not, strictly speaking, disagree with metaphysical answers to the question - since these answers are never verifiable, directly or indirectly, through the senses - those means by which I experience the world, and are not so by definition, I cannot consistently ask those questions at all. This is not subjectivism, but - mostly - logical positivism. As you are doubtless familiar with this school of thought, I take this reference to be a brief way of expressing my view. I know of no one who confuses LP with any subjectivist view.
Everything that has literal meaning, or that literally exists, is a particular. Generalisations are not a part of empirical reality - they do not literally exist. “Ultimacy”, for me, would be purely inductive - it would mean experiencing everything in the Universe - which is impossible, and trivial at the same time. It is not a logical operation at all, strictly. Where it is an abstraction, it is useful in language, for certain purposes (like economy of expression) but not in epistemology.
Metaphysics is, by definition, “meta”, or, yes “super” natural. Idealism is a form of metaphysics, of course. I have been, in the past, guilty of lumping all metaphysics together - I have tried to correct that, because while that actually has some use for a strict materialist, it can lead to a lack of clarity of expression. If I have done that here, I apologise. But these surely are examples of metaphysics, if not definitions.
This is a specific viewpoint, gleaned from Hume, Nietzsche and the LP’s, broadly. Doubtless I have explained it imperfectly.