That isn't necessarily a good thing and a huge setback on their sovereignty.
European countries need to become more independent form each other.
Militarization could help European countries in a lot of aspects.
That was the case throughout Cold War, somewhat, but there is literally no practical use for it now, aside form, perhaps, training and exercises.That nations still act independantly beyond this framework is because as long as no article 5 is invoked and it only was invoked very loosely against the Taliban, then all nations can act independantly and in their personal interests. The only base agreement is the mutual defense and that main assurance is not article 5 but e.g the US putting US soldiers where they would get killed if someone attacked another NATO member. Some of the reason of putting US, British and French soldiers in Germany were not about keeping Germany down somehow, but to guarantee germany that from minute one other NATO soldiers would be fighting and dieing in germany so none would bug out if germany were attacked. This was an important guarantee so West Germany saw no need to find an indvidual agreement with Russia or militarize excessively herself.
It is a huge burden on taxpayer, who not only has to pay for vast military-industrial complex expenses, but also to maintain and support armies of dwarf-states of Eastern Europe.Overall beyond its immediate defense agreement it has far more integration between nations concerning security beyond simply where to invade next or who the enemy is.