That 100KB feed is served by GitHub Pages, which should be pretty efficient - it gets gzipped and comes with ETags/last-modified headers, so good feed readers should be able to access it efficiently.
As a consumer of Atom feeds I find whole content feeds like that quite convenient, provided they don't get into the thousands of entries.
(Fun aside: I got the new Gemini 2.5 Pro to write me a quick Python script to confirm that GitHub Pages does indeed support gzip and ETag/last-modified: https://gist.github.com/simonw/7f6b167bd8288dccfbebbaf7e143e... )