But I am confused about how this relates to Visa and Mastercard. Those systems are used for payments between parties that have not necessarily established trust.
Yes, but more importantly, it's essentially the EU version of Alipay (which can be used for merchant payments as well as P2P transactions).
P2P payments, specifically SEPA Instant bank transfers, have already been instant and free for several years now in the EU, so there's no need for a Zelle alternative (other than maybe for contact discovery without IBAN).
And speaking of Alipay: This is the actual global alternative to Visa and Mastercard that almost nobody in the west is talking about or even aware of. While it used to be mainly used by either inbound or outbound tourists in/from China, it now spans many countries and issuing and merchant banks all over the world, including many in Europe. Wero is many years behind in that regard.
Plus some additional features like payments through QR.
These are two different use cases. I do not think anyone in their right mind is using Zelle to send money to a party they do not fully trust.