Paypal is quite popular in Germany but with Wero that popularity will decrease significantly. I expect that all around the Europe.
I have not tried Wero, but I have tried the german predecessor (paydirekt/giropay). It was ... not much less smooth than PayPal.
But I’ve only ever seen a single vendor offering it. 0 for Wero so far.
I like your optimism.
I don't know if popular is quite the right word. It certainly is widely used though...
Paying with Paypal is as easy as logging in. With Wero/iDeal you always need a phone or a code. People trust PayPal more too.