I've never been anywhere where I legitimately had signal but no data. When it seems to be connected buy isn't, sms mostly also won't go though. I also think there are less "remote" places in europe in general.

You just don't. Their adoption of Whatsapp(at least in Spain), seems to have been driven by a period in time when WhatsApp was coming up that the plans sold by cell service providers were near unlimited data, but only X amount of calls/texts allowed to be sent per month.

In the USA we had opposite plans during this time. Unlimited talk/text, but strict data caps.

Well, with imessage being on topic, apple seems to be really terrible at changing to sms when someone is not available online — I ran out of internet data once and tried to text my girlfriend on imessage assuming it will just send an sms, and it just waited for like 10 minutes before telling me it couldn’t be sent. The other side is even worse - I would have assumed apple checks whether the other half is expected to come online anytime soon and if not, send an sms instead. Nope, you just don’t get a message and are expected to long press and send as sms manually.

With 4G taking over, this will no longer be a differentiator, as on 4G SMS also goes over data (via VoLTE).

At least where I live, 4G got deployed on the low bands freed up by the digital TV switchover and hence has the best reception in remote areas.

In most of the world you do have either wifi or data coverage.

Usually, if you don't have data for signal (as opposed to run out of data in your plan) reasons, then you don't have signal at all, even for SMS, either...

And I have been to a number of islands across Polynesia and Micronesia where the cellular service simply does not exist; however, there is always Wi-Fi in hotels. SMS is of no use in such places.

You don't. But in the US I'm rarely in a place where I have no data but SMS still works. And Europe has more effective telecom service.