Feels like you weren't able to have a proper discussion with those people. In many EU countries, using SMS made/makes no sense because SMS was/is super expensive as compared to WhatsApp. And using iMessage makes no sense because most people don't have an iPhone. From their point of view, it actually makes no sense.

Now if you tell them "well, where I come from everybody has an iPhone" or "SMS have always been free", probably they won't say "still, I'm better than you for no apparent reason".

I don't think that it is actually seen as a mark of superiority anywhere in the EU to use WhatsApp. Unlike apparently in some places it is seen as a mark of superiority to have an iPhone vs an Android phone.

If you go in a EU country where SMS were not prohibitively expensive in the beginning of WhatsApp (e.g. France), you'll see that WhatsApp has been less successful (at least in the beginning). WhatsApp was a killer app because it was free SMS, really.