I think the better argument is that Europe has a credible nuclear defense, therefore they don't need conventional military. If Russia starts rolling tanks towards Berlin, drop a nuke outside their international waters and announce the next one will be on Moscow
How about if Russia starts sending troops to "protect" the ethnic Russian population in Latvia? Would the USA, UK, and/or France really threaten to nuke Moscow and start WW3 in that scenario? It's better to have a credible conventional deterrent and a range of possible responses instead of betting everything on an all-or-nothing nuclear response.