That's mostly a political/budget choice.
US: what, a bit over 300M people? EU: some ~550M? Both advanced economies.
US military might is a result of budget, raw manufacturing capability, and a glut of defense-related industry. Which (obviously) also sells their warez abroad.
No fundamental reason the EU couldn't obtain similar capabilities. But EU countries simply chose to outsource much defense design & manufacturing, apply a smaller budget, and rely on the US in several ways.
I'm sure some of this was regretted since Russia-Ukraine war started. Not sure if (given time) that's enough to bring EU up to military self-sufficiency.
So if both Russia and US were to fire their ICBMs in quick succession (mutually assured destruction) scenario, it’s likely the US ones will be a lot more potent. Most Russians are clustered on the west near Moscow.
US cities would still be hit and it would be very devastating, but Russia and China would be obliterated.
Death toll would be in the billions.