I didn't say it was a perfect solution and would be absolutely reliant on the 27 countries actually pulling together and fronting up with cash. However such a force, were it to exist, would have the ability to intervene in Ukraine and other non-NATO countries bordering Russia to challenge Russian aggression and expansionist policies.
NATO is constrained by it's founding principle of defence of its member states.
NATO is primarily constrained by its working principle of unanimous assent. It can - and has - operated outside the NATO area in response to a UNSCR, or even to a perceived humanitarian crisis. What is preventing NATO from acting in support of Ukraine is that the unanimous assent to do so is missing. Principally because the opposition is a nuclear-armed state headed by a mobster who is demonstrating irrational behaviour.
I can't see that principle changing massively under an EU construct. Look at the issues around qualified majority voting - can you honestly see the 27 signing up to allow the Commission to commit their forces to combat? All it would do is duplicate command structures and add confusion. It would also require the EU to duplicate the top end capabilities - and logistics mass - provided by the US (and to a degree the UK).