I don't think Wero can "win" this from just the merchants side. It's got to be better for the customer's side.
So when I from Slovakia want to buy something in a French eshop, I'm out of luck. And when on a vacation, can't use this system either, while a French person on a vacation in Slovakia can't use it either. My guess is people will mostly continue to use credit/debit cards.
Edit: oh, sorry, just realized you talking about international not domestic payments
There might be other instant QR payment systems out there though - I digress but on our recent visit to China we had to use Alipay as the cards are not accepted at most places and of course it works through scanning QRs, either you scan the vendor's code or they scan yours, and then you enter or confirm the amount and that's it. But the issue I have with these systems is the same as yours - we are fully dependent on our phones with no backup.
I agree this could be a difficult battle and we effectively need some alternative to existing card issuers if they are to be displaced.
Current contactless payments are easy, secure and allow disputes etc.
I mean, some places do that. But for the consumer there is no advantage. It's probably fine at cafés, restaurants and such. But why would you as a consumer want it for any more important purchase? As you mention.
The US is done as a global power, all their soft influence is gone, and the EU sees them as an adversary now.
Why would you think that contactless payment would require Visa or Mastercard?