I have read Nietzsche. In fact, I own several of his books. It is simply a matter of fact that Nietzsche didn't offer anything new to ontology or epistemology. Serious philosophers who may nevertheless greatly appreciate Nietzsche wouldn't even dispute that. Nietzsche isn't even known for anything related to philosophy proper. He is known for his ethics (which are malevolent in my view) and for his criticism of religion. It is also known that his writing quality diminished the nearer he drifted completely insane, which he did.
I think some of his insights are interesting, some of his historical criticisms, psychological insights and so on, but he was wickedly misogynist and hostile to any social equality and decency. I think that his interludes and maxims are more interesting than anything else he ever wrote and you can see for yourself what I'm talking about in various examples therein, such as within Beyond Good and Evil.
If I am stating that something does not exist, such as Nietzsche's contribution to ontology and epistemology, obviously I cannot point to something and say: "See, this is where it doesn't exist." Don't be silly.
Bertrand Russell himself, a reliable judge in things philosophical, observed that Nietzsche "invented no new technical theories in ontology or epistemology..." If you believe that you have found something that he and I missed, by all means present your evidence.
Two of my favorite Nietzsche interludes:
“It was a subtle refinement of God to learn Greek when he wished to write a book – and that he did not learn it better.”
“And if you gaze for long into an abyss, the abyss gazes also into you.”