It depends heavily on country, yes. USA is extremely light on WhatsApp, and MMS use is widespread (and has been free for a long time now, and SMS even longer). RCS is a mostly silent upgrade for USA.
I'm not sure which of the two is better tbh. Utterly dominated by a Facebook-owned system, or using something that's crappy enough that people spread out to a variety of systems?
Amazing how blinkered supposedly privacy conscious Europeans are when they willingly line up at the Facebook slaughterhouse.
The huge switch from SMS to WhatsApp in Europe was well done before they were acquired by Facebook. By then the damage was already done, because the network effects made it very hard to move away. By now, many people I know also have a Signal account, but it doesn't really get off the ground as long as, say, 30% of every group chat does not use Signal.
Year, back prior to the Zuckification I'd say it was a very clear upgrade for everyone in essentially every way. Dirt cheap (much less than even minimal texting), installable everywhere, adopted solid E2EE far ahead of basically every major player (2016!), it was great. USA had everything worse for a long time, and many things still are.
But once it landed in Zuck's hands, I no longer trust it one bit. Abandon ship.