I think this could only be a reality at a national level. Assessing military capabilities in relation to perceived threats is difficult. Sure there's critical defensive capabilities but military campaigns are rarely waged and defended in isolation. The fact that NATO is a thing is not only a factor of wanting protection but also because NATO members share intelligence, and in return receive a furnishing of troops and infrastructure.

Not saying it'd be easy for small, individual nations to counter coordinated attacks, but if the goal is defense, that's shared with the borders of nations next door. A coordinated response. When the likes of Hungary entered into NATO (post Soviet invasion) there's stimulus to a response. Now Hungary has to deal with the same thing again on it's doorstep due to the presence of, and to the expansion.

Don't know if you can agree with that but I see supranational policing as part of the problem here. It's not merely insulting outwardly and depending inwardly.