> I host a statically rendered wikipedia mirror. Tens of millions of gzipped html-files with a filesize in the range 1-5 Kb.

Have you ever tried Kiwix (https://www.kiwix.org ) and looked at the ZIM format (https://en.wikipedia.org/wiki/ZIM_(file_format) ), in particular those for Wikipedia (https://download.kiwix.org/zim ) ?