Based on that logic, 1/4 of our military should be in the desert and that's where we typically have fought our wars in the past several decades.
But this isn't a military decision, it's a presidential one based on politics. I agree that we don't need such a large force in Europe, but the same elsewhere. I don't think it's as much of a deterrent as we are led to believe. If Kim Jong-un gets the harebrained idea to cross the DMZ, no number of conventional troops in the south are going to stop that. That bloodbath will occur despite our presence.
Our current presence in Europe is not about WWII, it's about a commitment to NATO which was never about preventing the rise of another Nazi Germany. It was about the Soviet threat and while the name may have changed, that threat is still real and even stronger. Countering it conventionally during the Cold War was actually easy as it could be done simply through numbers, but we still haven't figured out how to deal with new informational today and it's hurting our ability to shape and influence that part of the world badly. Plus, none of this is about the overall mission of NATO and EUCOM, it's about Trump putting the screws to Merkel. Not that she doesn't deserve it, but his claim that this is all due to Germany not putting enough of its GDP for defense is ridiculous when the countries that will benefit from this move spend even less. Germany does have a stronger economy, but that is not the point. This is an emotional move by Trump and one that makes no sense.
And your point about a "33% manning boost" is moot. You act like the forces in Europe are not doing anything, whereas in fact they train as much if not more than those CONUS. That robbing Peter to pay Paul comparison doesn't increase our investment or capabilities. It may reduce the cost of having forces (it's cheaper to station people in some of the shitty assignments Stateside versus Europe), but it doesn't make us more effective operationally. In fact, I would argue the latter is the case.
Russia is kicking our ass informationally the same as China is kicking it economically. COVID has put a bit of a damper on it, but they'll adjust and survive; but I believe much of the chaos in this country is due to the amount of misinformation being pumped into it from abroad. To quote Agent K, "A person is smart. People are dumb, panicky dangerous animals and you know it." Society in general is gullible and will believe whatever the media (social or otherwise) tell them, and will respond accordingly as they don't know any better. Ever wonder how one dog can control and corral hundreds of sheep? Same analogy.
But anyone who thinks this move will somehow improve our influence worldwide is sadly mistaken. It's politics pure and simple, and costly ones at that. I've spent time at SHAPE and Patch, it will cost billions of dollars to accomplish and in the end nothing will change. And I didn't add a 'STS' to that as literally we the taxpayers will be taking it up the ass for this decision...