I don’t think any reasonable person can argue in good faith that Europe should rely on the US and Turkey in order to defend itself.
The EU is a bit of a mess, but I think it is a decent starting point for a defence union. The very reason it’s so hard to make it happen - constant vetos by random countries who are reluctant to accept the majority opinion - is also what would make it good. Abusing power (by for example attacking) would be difficult, but there is a strong common interest in defending the borders of Schengen.
I think the veto thing is absolutely necessary. The most important functions (defence when attacked, disaster relief) should be triggered automatically without political involvement should they ever become relevant; anything extra beyond core functions should be high hanging. If not we’ll have a European desert storm before we know it.
I have come to think that the only thing that is going to save Europe is how much we struggle to agree on anything. That’s a good thing in times when majorities are untrustworthy.