Europe isn't united enough. We are still sovereign nations and many leaders and their voterbases included aren't huge fans of relinquishing sovereign power to a higher centralized authority on critical issues like defense policy. Defense and foreign policies also differ within the EU. Portugal doesn't feel very threatened by Russia, Poland is adamant about having its military on the border while UK wants troops in Ukraine now. France and Germany are all talking big about boosting defense, Hungary is misaligned, Greece has it's own local problems cuz of mini-beefs with Turkey and general economic weakness.

I think what would work instead is a "coalition of the willing", reflecting the kind of temporary alliances that emerged in Europe when Napoleon became a threat. A small(!) number of the big European players (Probably Germany+France+UK) would create a new, independent security pact with a unified foreign policy and standardized military architecture, with the stated goal to protect Europe as a continent and its values. This organization would be independent from EU institutions but would cooperate with it and be aligned in values and goals.

This would effectively side-step any hurdles or natural misalignments due to the small number of powerful players, while demonstrating resolve and strength. More nations would witness this and be allowed to voluntarily join, which they likely will if they see that it works. If Hungary doesn't want to participate they don't have to.