"if an EU country is the victim of armed aggression on its territory, the other EU countries have an obligation to aid and assist it by all means in their power."

Technically EU wouldn't. But all EU members are obligated to send any aid and assistance in their power.

And that includes direct military support from those that have a military. Because it is in their power to give.

Also, add to that Article 222, the solidarity clause, that mandates Members to act jointly when an EU country is the victim of a terrorist attack, natural or manmade disaster.

Then there is the Lisbon treaty, article 42.

"When an EU Member State is the target of armed aggression on its territory, the other Member States must assist it by all the means in their power. Such commitments are to be consistent with the commitments made by Member States as members of NATO."

This could be interpreted as the commitments to the EU mutual defence clause, as the same as those of NATO article 5, from those that are part of NATO. Meaning, those who are members of both NATO and EU, must have a consistent commitment to both EU mutual defence, and Article 5. And since article 5 guarantees boots on the ground, so does the EU defence clause.

But I am not a lawyer, so take it with a pinch of salt.