RCS is not a Google product but the official SMS successor.
I still prefer RSS and I wish all blogs would have RSS. That being said, of course it's great if they offer ActivityPub as well and I hope both are used as wide as possible.
That's true, and I'm not a big fan of that either, I'd like to not have to rely on Google as well, but they do interoperate with other providers (for example with my provider) because it's a standard. I don't see how they discontinue RCS unless the whole standard fails to succeed, which seems unlikely.
And since they encrypt the messages, I see less of an issue with them providing the service, it's just store-and-forward of data they cannot read. Of course it would be best if every provider implemented RCS on their own and the Google backend would not be needed, but most of them dragged their feet until Google stepped in and enabled it for the rest of the world.
I don't think it's fair to lump RCS support in GMessages in with the rest of their products, even though I'm also skeptical of any product launches by them these days because they have a bad track record.
But what if it ... gasp ... RAINS?
Even you asking this question means you should not. Systemd is perfectly fine for most people and the people that dislike it have their very specific reasons. Just use what your distro gives you, you shouldn't have to care about these things.