Not quite sure about the On by default aspect; on my non-Google phone running stock android, it keeps asking me to enable RCS.
I keep clicking no because there’s a lot of ads pushed through RCS. This is annoying on top of the usual telemarketing stuff you might get due to phone numbers being sold.
Are you able to view YouTube at all with NoScript enabled ? When I tried it out last the page itself doesn’t load because everything is JS based.