So Etsy wants to replace a core part of their frontend tooling to save 30KB in bundle size?
You clearly didn't read the article. It mentions that in addition to the (relatively small) bundle size savings, the version of Preact they were investigating (as of 2020 when it was written) was also more compatible with the current version of React they were using at the time than the newest version of React (15 -> 16 had a lot of breaking changes). I don't believe the bundle size was really a major contributor to…
You clearly didn't read the HN guidelines, judging by this and your other comments.
> Be kind. Don't be snarky. Have curious conversation; don't cross-examine. Please don't fulminate. Please don't sneer, including at the rest of the community.