> Page is slow because the average page size is 2.2mb. Plus JavaScript parsing + execution time. Plus asynchronous calls to go load more stuff. Plus time to re-layout around the new stuff.

I think it's mostly blocking chains of multiple networks requests that execute in sequence (taking a network round-trip each time). I inherited a slow ~2mb frontend app at work, which seemed horrendously bloated to me. It turned out to be not that easy to reduce to the size (due to large amounts of code depending on large libraries), but it also turned out to be possible to make it load fast without reducing the payload size.