Yes, there are valid use cases for irreversible payments, like closing on a home. Banks do have solutions for this: wire transfers. Which is what you’ll use if you buy a house in the US.
Nothing in banking is un-undoable. Some just require more effort to undo.
As opposed to ACH which could bounce or you could issue a stop payment.
And for fraudulent transfers, Zelle’s trying to pin them on the customer is them hoping you’d give up rather than remind them that regulation E governs it as well, and they used to acknowledge that on their web site.