Instead it argues the opposite - scale back the reach that Brussels has to just trade and travel policy, leaving other countries free to pursue their own defense policies. You'd see an Eastern group of European countries (Poland, Czechia, Slovakia, Romania, Hungary, the Baltics) pursue aggressive defense policies while other outfits like Spain kinda just sit there.

I think that's unlikely, also. Remember, even the original Articles had some degree of coordinated military defense. There's a major free-rider problem - Poland probably doesn't want Spain to be able to get the benefit of their military expenditures, which block continental invasions from the east). There's also collective action problem - the Great European Plain is the "roadway" for land forces to get into Europe from the east, and so you need all of the countries that sit on that plain to be heavily militarized in order to provide an effective defense. There's significant reasons why Europe would want to maintain tight integration of national defense institutions and policies.

Plus, there's the pretty significant problem of what happens when you eliminate common defense systems and go back to having more nationalized armies again. Remember, many of the world's most terrible wars didn't result from Europe being invaded from without, but from wars between European countries. This is the "be careful what you wish for" scenario. The Pax Americana arose because Europe was under the massively powerful umbrella of the U.S. military....but it also existed in part because European armed forces were generally weak and subject mostly to NATO oversight. Getting Europe to vastly increase its own defense operations isn't an entirely unmitigated good, because you increase the chances of going back to the Bad Old Days of wars within Europe.