iOS does not currently implement end-to-end encryption for RCS. End-to-end encryption for RCS is exclusive to conversations between Google Messages users. Apple has said they'll implement the new MLS end-to-end encryption for RCS but has not done it and has provided no timeline for doing it. It took them a very long time to implement basic RCS support and this will likely take a long time too. Google Messages has not yet moved to the new MLS encryption, but it will need to do that too in order for iOS implementing it to provide end-to-end encryption across them.
For now, I have switched back to iOS due to a significant majority of my contacts using iMessage, so I'm back to encrypted chats again. Hopefully the future of RCS changes things while America struggles with using a unified messenger. I dream of using a dumb phone with RCS.
But they did share valid concerns about their reasoning and most other aspects of the OS certainly have a great focus on security.