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Is it actually universally E2E or only some? I find some reddit posts implying it's some.The E2EE on RCS is an extension to the protocol developed by Google. I don't know who has implemented it other than Google. So if a user is on a carrier that does their own RCS impl (many carriers piggyback off of Google's so they don't have to deal with it), they may not have E2EE.
> Do all RCS messages go through Google's servers?
If your carrier isn't using Google's implementation, and you're messaging someone on a carrier also not using Google's implementation, then it won't go through Google's servers. Otherwise, it will. In theory, this won't matter, assuming the E2EE is implemented correctly and securely. I don't know if an audit has been done, though.
There's also the case where one person is on a carrier using Google's impl, and the other is on a carrier that is not, and that carrier has not implemented E2EE. Then the message will go through Google's servers, and Google will be able to read it.
This is how I understand it, anyway; I don't intimately know the details of the protocol, so this might not be 100% correct.