Comment by Elfener
19 days ago
When you use Whatsapp, you're trusting a single entity to handle your messages (plus your ISP I guess). When you use RCS, your messages go through your mobile operator, google, and perhaps someone else in an overly complicated way that is also built upon SMS (a non-internet thing) for more confusion.
Message payloads go directly to Google servers, there's no difference in practice.
Carriers handle IMS registration, that's it. And not even in all cases.