2017-2019 has not convinced me most voters are willing to look beyond the end of their nose. Where was the EU action over Crimea?
One could reasonably argue that Ukraine simply wasn't part of the EU, and if Russia threatened Poland it would be a different matter. That it is the EU membership, not the buffer zone, that is important.
Another possible interpretation is EU would have wanted to intervene, but its current political structure proved too deliberative to react before it was too late. That would imply an EU army would also need political reform.