You're also massively wrong about DirectX on Linux, DXVK and VKD3D both work to run various versions of it on Linux.
I very clearly wrote that Linux does not support DirectX. Which is 100% true, no matter how you look at it. Just because there are translation layers, it doesn't mean Linux 'supports DirectX', because it doesn't. It supports Vulkan, which DXVK and VKD3D translate DirectX API calls to.
Let's say you can't read Spanish, but you hire a translator to translate a text for you. Now you can read it. Does that mean you can suddenly read Spanish?
The problem is, the EU isn't united nearly enough to fight a war together. If, for instance, Russia attacks, it'll be mostly Poland, Lithuania, Latvia and Estonia defending. Maybe Romania too, and maybe with some support from the rest of the EU. As it stands right now, the EU is divided on many issues, with some countries (notably Hungary) intentionally sabotaging it from the inside.
Even if - and that's a big if - all or at least most of EU member states can come to agreement and cooperate in a conflict, our militaries aren't very well prepared to work together. This would require years of cross-border military drills between all of the member states. Especially considering the fact that the vast majority of all EU soldiers have never seen any real combat. Russia may be losing a lot of soldiers in Ukraine. But those who survive become extremely valuable assets for the military, since real world combat experience is infinitely more useful than textbooks or casual training exercises.