Third party apps can't even SMS on iOS. On Apple's platform, you use their apps or you don't get the feature. The iOS implementation of RCS doesn't even yet support encryption. Apple is testing encryption between Apple devices.
That Apple and Google both hold the keys to what started out as an open GSMA standard, and now have a closed-source platform screams never trust it.
The former was a truth, the latter was a (poorly-placed) joke about how IRC could be noisy chaos with bots and ping floods and giant ASCII art messages. I'd take the latter any day.