RCS doesn't really do a whole lot of anything. It's a step up from SMS/MMS, but not by much.
All the features people think they mean when they're talking about RCS are proprietary Google extensions that only work if you go through Google's servers. They're basically exactly the same as Apple putting iMessage on top; Apple just brags about it while Google tries to trick you into thinking incompatibility is someone else's fault for not giving them control.
Usually I’ll defend Apple on this, but yes it’s a step up from SMS, and Apple is a big reason RCS hadnt been widely adopted as a replacement, and incremented to include more features.
I’m definitely on Googles side here: years of no one doing anything until “fine, I’ll take care it myself”
That's precisely what E2EE is supposed to prevent. If the phone company gets hacked, attackers can see all the traffic going through all of their towers, so if everything is encrypted before getting to the towers, they can't see the contents. IIRC, metadata like phone numbers can be read though, so they can see who you're talking to, but they can't see what you're saying.
The phone manufacturer, however, can see everything before it's encrypted and after it's decrypted.
At this point you have to assume that if you are not using your own install of custom Android ROM, your end point is not secure beyond keeping stupid criminals out