The intended purpose of RCS was to be federated between carriers, just like SMS. If you centralise it then it's just a worse version of any of Google's abandoned chat apps. But there's a realpolitik reason to insist on centralised RCS: because it's already got the reputation of decentralisation, it makes it look like Google is better than it actually is.
reply> The intended purpose of RCS was to be federated between carriers, just like SMS.
replyOof, so it was essentially destined to fail when the spec was being written.
Did SMS fail? Sort of, as it's rarely used, but also not, because it continues to work and it's still the only federated messaging system you can rely on being available on your phone (besides phone calls).
replySMS was a huge success. For a standard that was defined in 1986 and first rolled out in 1992, it had good longevity and was extremely popular from its introduction until ~2010 [1]. Nearly 20 years is a good run for a technology in a rapidly evolving field. It was also designed in a completely different age when most phones did not have cellular internet and carrier support and federation were the only way to provide reliable person-to-person messaging. Even though the carriers probably dream of reviving SMS as RCS to be more than just pipes for the internet, those days are over.
replyGoogle-based RCS is Google coopting an existing standard to get the foot in the door for Apple Messages interoperability. By coopting a standard (rather than pushing yet another Google messenger), they could convince regulators to push Apple towards supporting it. Otherwise RCS is completely irrelevant and if it weren't for Google, it would've been mostly dead.
[1] Yeah, I realize that is was probably used in the US much longer, but that's when it started to dwindle in the rest of the world, where MMS also never really took off.