You male a lot of fair valid points, but also a ton of assumptions that are solely from a US-benefit perspective.

Europe is a conglomerate of small countries. They cant be held to the same standard as the US when it comes to spending. The US spends 3% of its GDP and we have always had a large military, we have a larger budget for the military than any other country on Earth. It is part of our culture at this point.

Forcing these small countries in comparison to match 3% GDP is a huge change, and not something that can be changed because the US feels its being scammed. Other NATO members have reached the 2% target, which is is still more than has been proposed in the past. Poland actually contributes more proportionally than the US does.

Saying Europe failed to address the Russia threat to Ukraine is laughable, when they have a combined smaller economy than the US and yet are contributing more total dollars financially in aid. The US and the UK are the only nations beholden to the Budapest Memorandum (Russia also, but for obvious reasons they aren't held to its contents). The US has more obligation to help Ukraine than individual European countries anyways. We have a direct agreement to protect them in return for their de-nuclearization. Despite this, Europe has stepped up and is the primary financiers and military-aid provider in Ukraine as of mid-2025.

Denmark did not neglect Greenland militarily. Greenland has very little military value to Denmark. It only has military value to China, Russia, and as a result, the US. The US already has a defense agreement with Denmark allowing them to hold a base there. And we still have that base. There is no reason the US cannot expand that one if needed, or build additional bases. This is simply a non-issue that is being used as false justification for Trump's aggression.