I think we're partially missing each other's matching meaning on some of this lol

But, Google has not allowed any app developers to access RCS. You know how there's qksms, textra, chomp, etc? All those developers were chomping at the bit to either make new apps, or extend their old ones. But they can't. Google simply doesn't allow access to the service. I haven't used an oem app for sms in years tbh, they tend to suck hard, and since many oems just ship Google messages, they definitely suck hard.

RCS is meant to be at that same level, where it's a carrier linked service. Currently, all the us carriers have it implemented afaik. How well, I don't know because Google messages sucks.

Carriers used to deploy messaging apps of their own either beside or instead of OEM apps. T-Mobile kinda does, but only if you have multiple lines. I have it on my phone because I got hornswoggled into doing some local shit that I needed the extra line for. Sprint had one back maybe twelve years ago? Hard to remember which phone I had their app on. It sucked. So I didn't use it. The LG app sucked too on that phone. Switched over to a more defunct sms app and never really used oem stuff again, so I didn't notice when Sprint did away with theirs, but the phone after that didn't have it.

All Google would have to do is open up the API for RCS, and there would be a shit ton of apps made for it.

What that all means is that Google has pushed their foot into carrier messaging, if we want to use RCS. They've got their own app being the only way to access a carrier feature that we pay for. Them adding encryption to that is a joke.