I'm guessing all the people suggesting to ditch WhatsApp have never been to Brazil. Everything there is done with it, you can buy groceries, medicine, do banking, get services, take out, etc... Getting the whole country to change will never happen. So, yes, while some of us do install Signal, none will ever uninstall WhatsApp...
The UK isn't quite that far, but it's absolutely the dominant text messaging and calling app in the UK. Nobody uses the built in Android or Apple tools anymore, and I'm as likely to receive a WhatsApp voice call as an actual phone call these days.
I have Signal on my phone, but I've literally never had a cause to use it; I've simply got no contacts on there.