Your view of "biggest is winner" is totally wrong. There is nothing wrong in supporting those small countries, they won't require you to move all your army to defend them. In fact, just by being allies keeps the peace, at a very low cost for both parts.
You have a very small frame. If you let Russia, for example, take all those small countries for free, suddenly you have a bigger enemy. Not saying that they would defeat the US, but they can make worse problems. Because those little countries you despise are historically peaceful, but Russia not so much. Because Russia leaders are unreliable, for example: https://www.newsweek.com/what-putin-has-said-about-russia-ta.... By keeping Russia at bay, the USA keeps the hegemony more easily and for less money.
Please, stop thinking that USA is "bankrolling" no one. USA spending on defense of those countries is basically zero. It's just a few military bases with a few dozens of people (20 in Bulgaria, 20 in Estonia, 20 in Finland, 20 in Latvia, 20 in Lithuania, 200 in Poland and 130 in Romania, the countries you named), and have nukes at home that they were going to have anyway. By contrast, those countries deployed to Afghanistan in Operation Enduring Freedom, answering the USA call: Bulgaria 600, Estonia 250, Lithuania 270, Poland 2500 and Romania 1800. It was a bargain for the USA.
> Goodbye military industrial complex? Hallelujah!
I never said it was a bad thing per se. I only say that being an unreliable supplier of military goods makes you an undesirable business partner. A large share of the GDP of the US depends on military exports, so a large part of the population would have to find another job. Again: this is not bad per se. But, are you sure you (the USA) want this? How many Trump supporters and isolationists don't even suspect how much of the GDP is based on military exports?
Another unintended consequence might be China becoming a more reliable military supplier than the US, thus empowering their military industry. Are the USA interested in that happening?
Another consequence might be Europe becoming a significant player in the military industry, effectively moving jobs and GDP from USA to Europe.
> It's more absurd thinking
It was not about GDP, stop thinking in pure economical terms if you want to talk geopolitics. It was about influence. China has always been a wild card. But the USSR had a lot of influence over half Europe, half Hispan-America and half Africa. It's not about economy: put and support a dictatorship in a country like Cuba or North Korea, and it doesn't matter how uber poor they are. You now have two pains in the ass, one of them with nukes and ICBMs, the other was once very close to be a nuke base pointing to the USA.
For years, for decades, it was the USA who pressed the NATO expansion. It's imperialistic people like Putin the one who despises it. Again, you can be isolationist like Switzerland is in many senses, but then don't complain when others don't buy your shit, or develop nukes, or make friends with your enemies, or make alliances among themselves (like https://www.france24.com/en/europe/20250226-trump-says-eu-fo...).