That being said, it is not clear to me the benefit of the USA remaining in NATO
The benefit is obvious... benefit to Europe, that is. It's so warmongering Europe can pursue aggressive foreign policies that further their interest, with the assurance of US support. They get to benefit from our military, without having to pay for that capability themselves.
Europe as a whole has been fighting itself for the past 1000 years. Early America was smart enough to leave it behind. Would that contemporary, globalist America were half as smart.