The fact that this wasn't a three day operation is in large part sure to the US. But your portrayal of the facts makes no sense. Nobody is forcing Ukraine to ask the US for help (except Russia). The US obliges because it does align with their interest. But in the end, all international help at scale is motivated by national interest.
Testing out new battlefield technology before the next Great War.
Should a nation only fight with pre-agreed equipment that is at least of a certain age?
Unfortunately for the people of Ukraine the geopolitical motives and interests of the US don't necessarily align with their interests.
Well, they for sure don't align with Russia's.
Like Chomsky says "we will fight them to the last Ukrainian"
Or was it North Korean?
Military deployments aren't "meat grinders" for your own troops if they're well-equipped and trained. That's the whole point of western militaries.
War is shit. But as an ex-soldier: you know what you sign up for. I also expected it during my service, though it never happened.
It's like saying calling firefighters to rescue someone from a burning house is only acceptable if you ran into it first. It makes no sense.