Why is it presented as a given that the EU has failed and that its model is dead ?
it's not that the EU as a whole is dead, but a particular version of it (ever greater integration, euro in all countries) is dead because no one wants that anymore (though those in charge of the EU don't seem to really realize that yet).
The Euro has failed because that's all it can do. There is no way to make a non-transfer union with no shared fiscal policy between Germany and southern Europe work.
There is no evidence that the majority of EU citizens want ever-greater intergration with more and more decisions that affect their lives being made by unaccountable technocrats in Brussels.