Firebase API has gotten slower over the years. That affects Interactive time and lighthouse score. Preact HN uses their own servers, and React HN uses the Firebase API.
Also, some passes site is progressively enhanced check because some elements are rendered without JS. Which results in higher score.
Preact HN loads offline but without content. Lighthouse assumes that app works offline, but in reality app is useless without actual stories.
I use Firebase API in my web app (https://hn.premii.com/) and scrap YC in my downloadable app (https://hn.premii.com/about/). Both has different actual and perceived performance.
Write operations are not possible with HN clones as there are no YC apis. They should build reddit clone. I have build reddit clone https://reddit.premii.com/ using their official APIs.