I'd go even further in explaining it (if I understand correctly), in that sms/mms interoperability is a core carrier item/function, a layer just beyond no different than how they provide core voice call interoperability, and a layer beyond the provision of a "data connection to the internet". The phone manufactures basically have nothing to do with control over sms/mms, other than needing to implement phone and text apps in their phones that will confirm to what the carriers prescribe for a device to operate on their networks (plus of course the big time lobby pressure leverage that the manufactures have over the carriers, or vice versa). RCS and iMessaging (WhatsApp, FB Messenger, Telegram, Signal,.. pick one's whatever favourite messaging app) however are completely opposite. The carriers are completely out the loop as all those services are simply just using the "data connection to the internet" the carrier is providing, in a crude sense no different than when user's browsers interact with web servers. For sms/mms, the arrangement is between the phone user and their carrier. For all the data connection driven messaging apps, the arrangement is between the phone user and the TermsOFService of the app provider when one signed up for an account.
The safety aspect comes in (in my opinion) as related to the complexity of how sms/mms or data connections are served up. Lots of folks, for example, will still be able to send sms/mms and make voice calls even when there are big data network "internet" outages, or send sms/mms even when they can't make voice calls. That's a good thing. In an emergency situation, we probably don't need to still be able to send grandma a massive video file, but it is almost critical to still be able to reliably exchange short status updates, like confirmation that she's still alive or if her oxygen tank is running low. Well, that's how it's all supposed to work (in my opinion), but as we saw with the big recent Rogers outage so much stuff has been now pilled into "data connections" that when something goes wrong with it, there are now massive ripple impacts to many things.
The other aspects of safety related to sms/mms is security. From what I understand, not much security is involved with sms/mms messages right now. So, some sort of additional mechanism for authentication and then also security of the actual contents of the short messages would be nice. Those aspects of security are already addressed if one is using iMessaging or RCS or Telegram or many other data connection messaging apps. However, the service model for all those data connection messaging apps (including iMessaging and RCS) is wrong (in my opinion) for safety critical communcations, because we shouldn't have to rely on the TermsAndConditions with WhatsApp or FB (or Apple or Google) for example, those companies aren't in that line of business as related to safety criticality services (not sure the Telcoms are either anymore however).