More important is that Greece is part of the EU while Turkey is not, and EU members are supposed to come to the aid of any member that is the victim of military aggression.
Many Ukrainians regretted not being part of the EU when Russia invaded.
Not so true about EU, as EU has no common foreign policy or army. On the other hand if a NATO member gets attacked its part of the treaty that others come to help, the problem in this case is that the attacker is also a member and I don't think it's clear what happens in that case.
NATO is more and more an empty shell organization. The real question is: will other European nations side with Greece and help her militarily in case of an armed conflict? I’m particularly concerned with the position of France, which has one of the strongest EU military and possess an aircraft carrier. The political leaders have no balls however and they could realistically let Turkey invades part of Greece without moving a finger. The second issue is Germany position, which not only has historically been allied with Turkey, but also hosts a huge Turkish diaspora, and could political veto EU decisions.
Many Ukrainians regretted not being part of the EU when Russia invaded.