I'm fairly sure the only reason for which Apple is using RCS is to circumvent the EU DSA, which requires them to make iMessage interoperable with other chat systems. So instead of opening access to iMessage they're using a completely different system as a distraction.
I mean, they could've said that iMessage is already interoperable via SMS but the feature disparity is too large. RCS will serve nicely to confuse the issue.
There's otherwise nothing to gain for Apple by adopting RCS. iMessage already does everything RCS does and more.
They could also kill RCS tomorrow if they wanted to, by simply releasing iMessage for Android. But then they wouldn't have a red herring to show the EU — if anything they'd be in an even worse position as per DSA. It would also antagonize Google although I'm not sure how much they care about that.