Devil's advocate for why ontology is meaningless and vacuous.

[Gemini]

I've given up defining "existence" and "reality" in non-circular terms. I've not seen it done. I use them only comparatively, or informally. Hence absurdism

I think if the question is "what does reality mean," in some rarified, ethereal, meta-philosophical sense, then you're right. If the question is, "what's a useful definition of reality?" that's answerable. 

Features of a map that don't correspond to any territory aren't real. Which could be epistemological instruments, fictional entities, or delusions. I know that "centimeters" have no existence apart from representational systems that we use to schematize experience; the character "Gandalf" corresponds to no historical person; and conspiracist ideation pertaining to reptilian-human hybrids is madness.

All of these beliefs do exist in a sense, as the part of the territory that the map is made out of (whatever constitutes experience), but they don't correspond to anything other than themselves.