Article 5 is the shield that drastically decreases the amount of nuclear weapons European nations need to deploy, because USSR / Russian inventories are balanced out by American inventories, if it comes to all-out war.
Consequently, the world as a whole is a lot safer because {flight time Russia-US} >> {flight time Europe-Russia}, which allows for additional fail-safe guarantees on weapons that there wouldn't otherwise be a time budget for.
The US stations some of its nukes in Europe, so the flight time is less than you think.
Also, it is widely believed that the US has an “understanding” with certain European countries that in extreme circumstances (aka World War III) the US will hand those nukes over to the host countries, and then the host country governments will decide for themselves what use to make of them. In part, this helps discourage nuclear proliferation-Germany or the Netherlands don’t need to make their own nuclear weapons because they know if they ever really need them, Uncle Sam will help them acquire them real real fast (“here’s the keys to the safe, good luck”)
As far as I know, the US hasn't stationed M/IRBM or nuclear cruise missiles in Europe since the early-60s Jupiter MRBM [0] and GLCM [1] were withdrawn.
[0] https://www.theatlantic.com/magazine/archive/2013/01/the-rea...
[1] https://en.m.wikipedia.org/wiki/BGM-109G_Ground_Launched_Cru...
I have to wonder to what extent the development of these alliances might have been influenced by the concern you raise though, you raise a good point.