I my mind, YouTube did not prematurely optimize.

1. They took full advantage of DMCA and pirated videos made easy home there until copyright notice came in. No technology to try and do it before upload, no pre publish human intervention.

2. YouTube player was just better, especially with most of the globe on dial up. It would let videos buffer for hours until 100%, even if you had a disconnection it would just restart downloading as it should. Won’t just stop after some time to preserve bandwidth. Once downloaded, videos won’t restream and you could easily move on timeline so long as you kept the browser window open. None of their competitors did this as I recall and were preserving bandwidth they would never get to use.