TMH, should only load a relatively small amour of code to support dynamic injecting of video for thumbnails that load the player on click and what not. But we can be sure to reduce this to an absolute minimum in the upcoming player v2 upgrade.
And clearly we should remove the 1k or so in the startup that is reloaded frequently. That startup code was focused on micro optimization against payload size, I.e not loading timed text library if in-page videos did not have timed text. But we now know / think its much better to have a slightly larger single payload for "video" and not have micro optimization logic being loaded all the time.
I'd recommend measuring some non-main-pages as well; that JavaScript payload seems to be reduced by about half if you load some other random page on Commons.
It looks like TimedMediaHandler is loading a lot to initialize a video that might never get played, for instance, while it never gets loaded on a page that doesn't include a video on it.
-- brion