Obviously Wall Street would have preferred purchasing from US-listed/owned arms companies, but from the perspective of a military alliance, having well-armed allies is the main point.
It's really hard to argue with Trump's methods if they led to Europe finally spending on their own defense.
On the contrary, his methods are ridiculous. He could have achieved similar ends without kowtowing to Russia, without squandering the opportunity to further weaken Russia’s military capacity, and so on. Something similar applies to pretty much everything else he’s done. He incurs collateral damage on everything even when it’s completely unnecessary to do so. It’s a definitional example of egregious incompetence.
The fact that they are doing this because they don’t trust the US to honor its commitments is a very different proposition from “maybe it’s for the best”.
And if you’re familiar with world war 1 and 2, you might doubt that significant increase in domestic military production is a wholly good thing.
But point stands: it’s an example of formerly-strong alliance that is no longer trusted.