I am under the impression that an unstated design objective of gemini was preventing eternal september by trading it off for staying an eternal echo chamber tobe inhabited only by people smart enough to write their own client and server software.
It's limited to those that are primarily interested in text (and the occasional image). Which probably prevents it from ever going mainstream (and thus an eternal september). What it's generally sacrificing is interactivity.
That seems like it's shooting more for the early internet. Which, yeah, has quite a bit of overlap with people who can code, but not as much as you're implying. And I do remember quite a few echo chambers on the early internet, but I remember a lot less of them without algorithmic feeds. Just by chance, you'd end up running across a bunch of people who disagree with you on a lot of things.