Article 42.7 doesn’t guarantee a joint military response ( trust me, we had two whole referenda about it). There’s also the fact that without joint training and equipment standardisation prior to any action, how much more effective will you really be?
As most EU states at the time were already in NATO, it was less critical. Now, and in the near future if Moldova and Ukraine applications are approved, it could mean something very different than what was envisaged. At the time, a large scale European land war was not what was envisaged. Even without committing arms and troops to a fight that was recognised as an EU action, by providing indirect support would you still be recognised as a combatant?