The opposite is true.
NATO is a defensive alliance, not an offensive alliance. When the US invades Venezuela, Iran, and Cuba, NATO isn't suppose to help our offense.
Hence, their lack of participation in Iran means nothing.
It meant a lot when we were attacked on 9/11, when NATO came to our aid, spending $500 billion and thousands of their soldiers lives to help us. They were and still are willing to help DEFEND us.
We don't pay anything for the defense of Europe. Our military spending wouldn't go down if we left NATO, it'd go up.
Even if we weren't in an alliance, we'd still defend Europe, just like we did in WW I and WW II. If Russia or China attacked Europe, we'd still come to its aid, even if we weren't in NATO.
I'm not sure they need us. If the war in Ukraine has proven anything it's that Russia isn't a military threat. They are too corrupt and poor to mount a serious challenge to Europe. China's threat is likewise fairly remote. The only country that has threatened European territory in recent years is Trump's America.
Overwhelmingly, the most important thing that NATO gives America is LEGITIMACY. Otherwise we are just working solely in our own interest that sooner or later everyone in the world will line up against, in much the same way they line up against Putin's Russia.