That's not the reality though, correct? When I send a message to a friend using the Messages app it's being sent as an iMessage if both of us use an iPhone. I don't care what the format is, my intention is to send an SMS. So you can't use this as evidence of popularity of iMessages.
Just looking at my message list: at least 40% of my messages are alerts, reminders, payment confirmations, etc. Are you saying in Europe people get those via Signal?