GitHub seems to be the worst of both worlds - partially rendered on the server, but then the frontend inexplicably pulls in additional data like... commit messages??

It's a double hit of latency, and for bonus points, the commit messages won't load at all if your browser is slightly out of date

It was. Open a huge diff in it now and go grab some dinner while your browser tries to render it.

I don’t hate GitHub or anything, but its UI is way slower now than it use to be.