I think that the specifics of the protocol don't actually matter all that much. What matters is that it's sufficiently unappealing to filter out most potential users; you genuinely have to feel strongly about the state of the web etc to spend a lot of time on Gemini.

In that sense, I suspect that OP is right and they could have achieved the same on top of, say, HTML 2 (https://www.rfc-editor.org/rfc/rfc1866).