Poland with like 40 million people has way less than 100 front line fighters. Nobody has spent anything on defense in that part of Europe and now it is biting them in the butt. Freedom isn’t free as they say....
There’s probably a balance to be struck, and it has to be reconsidered regularly for each individual country. An advantage of not having all our allies armed to the teeth is that such cuts down on “adventurism” in which the ally assumes that if something goes wrong, the US is treaty bound to come to their rescue. This is a related argument to my point that if the US cannot be depended on to provide a defense umbrella / honor its security arrangements, Assurances, and Treaties, there will be nuclear weapons proliferation like nothing we’ve ever seen, and that almost certainly leads to a significant nuclear exchange in the not too distant future. Such WILL affect us, even if its “only” via radiation drifting our way, and economic effects.
On the other hand, there is nothing wrong with us insisting that countries capable of footing the bill do so, with us as essentially the volume discount hired guns.
That said, then there are the cases where the economy of the country(s) are not sufficient to foot the bill. I’d have to research and do some math, but while “doing ok” now, I don’t think the Baltic countries you add up have remotely near the GDP of Singapore, or even Finland. Estonia in particular seems to be on the right track with their economy, but their economy is tiny: GDP (est.) was $28.44 billion in 2012 (PPP). By comparison, Singapore’s GDP in 2011 was (est.) $318.9 billion (PPP), and the country is flat out dripping with wealth, infrastructure, you name it. The Soviets left Estonia a wreck, while Singapore was already booming at that time. So the comparison is hardly fair.
In such a case, I think the answer is that the ally provide the troops, we provide bargain basement (but good) equipment and training, and we get basing rights (which will also help their economy.) Others may have even better ideas - what do you think?
I agree with you that all of Europe needs to spend much more on its defense and they could easily do so by pooling their resources and finding the right niches where each nation already excels instead of duplicating efforts. But one thing I think you do over look in comparing Singapore national defense efforts and spending to the Baltics is that Singapore was not held back by communism for over 50 years. The former Soviet Satellites are still recovering from Soviet/Russian domination. And as for Ukraine, they were not allowed by Russia to spend enough on defense to be anything but weak.