If I understand, these other players can't parse a youtube URL (or video,
whatever parsing exactly means). the -g options does that for them, is that
it ?
I just found yet another option, sinc MPV integrates youtube-dl for streaming
URLS: https://addons.mozilla.org/en-us/firefox/addon/watch-with-mpv/
Might be worth using for anyone who wants a simple way (and simple to
install) to play videos without javascript/flash/html5. No scripts or
anything.
I personally like the scripted way more, because it's also browser-agnostic.
Thanks again for your help everyone.