WhatsApp is a closed protocol owned by Facebook. It has its uses but relying on it is a mistake.
https://www.statista.com/statistics/271561/number-of-sent-sm...
The stats show a significant drop as mobile data became cheaper and richer services became available, but still quite a lot of traffic.
I suspect that the people I see using Nokia and Samsung dumb phones will continue to use SMS, so traffic will fall to a sustained tail.
https://www.statista.com/statistics/271561/number-of-sent-sm...
There's a lot of people here claiming that their personal use is representative of their country, or of Europe as a whole. I get SMS from a lot of people. You don't, probably because a lot of the people you know are on Facebook/Whatsapp and it's more convenient for them to stay with that platform. That doesn't mean that they don't use SMS for anyone else. It just means that you are bubbled.