That's true, but at the same time it was probably already the case before invasion of Ukraine, and it is definitely the case now.
The main issue is political fragmentation: would Paris and Berlin risk lives of French and German people (soldiers and civilians due to retaliation) to save Vilnius?
But if the answer is true (as obligated by the Treaty of Maastricht, independently of NATO) then Russia stands no chance with conventional weapons against the whole Western Europe, the balance of military, demographic and industrial power is ridiculously lopsided (involving nuclear weapons would also raise the same political question about the French willingness to nuke Russia in retaliation to Russia nuking Poland but if the answer is yes, Russia cannot win a nuclear war either (which everyone would lose)).