That doesn't matter though. Again, the mutual defense clause binds the entirety of the EU, to aid and assist any member country that is victim of aggression on it's territory, by "all the means in their power". Meaning, not only economic sanctions and weapons, but inevitably also by providing full fledged military support.
That argument is built on fallacies imo. The EU does not require to form an ad-hoc uniform army over night, to repulse Russia. That's not the case with NATO either. There is a reason interoperability exists and joint logistics and maneuver exercises are being carried out for decades. I think you might be underestimating EU militaries joint response capabilities, in case of an attack. Secondly, we see Europe's resolve in aiding Ukraine, despite Russian economic and military, even implied nuclear threats and counter-sanctions. Germany ignored them. Yes, not everyone hopped on the Bandwagon for various reasons, but most European countries provide at least humanitarian aid, the majority also weapons, including Germany who is now sending heavy weapons too, despite a series of Russian threats. They even decided to switch to alternatives, just because of this conflict, and the message couldn't be more clear:
This is, in response to a war of aggression against an outsider, a nation, that is neither EU, nor NATO member.
I think, if anything, that's a good indicatoin, that the EU would tolerate Russian aggresssion against it's members, considerably less.
Neither would Russia want to risk nuclear war either. Europe has nuclear weapons too. France and GB have their own arsenals, with hundreds of warheads. There is just no chance for Russia ever winning a war of aggression against Europe in their current state, even if NATO didn't exist. If they escalated it with nuclear attacks, they would be attacked as well and then it's Game Over for everyone.
It's not a question to me wheter NATO still served it's purpose. I think it does, regardless of wheter the EU itself had a mutual defense clause or not. But the cause exists and it's also a garantor. Ofc, without NATO, which brings an entity as powerful as the USA onto the playing field, the EU would be weaker by default. But not remotely enough for Russia, to consider going full tard.