Good post, MrSaturn.
You've shown the similarities between "then" and "now" but I believe that two factors separate "now" and "then"...
First, the enemies we fight are not even close to the enemies we fought in WW2. We have never fought a whole nation since then, in my opinion. We didn't just fight the government of Germany or the government of Japan. No, they, like us, had almost every citizen doing their duty to help them. They didn't roll over and die after an air campaign or hide in the jungle/forest/basement. They fought tenaciously; they had honest-to-God navies, competent air forces, and professional armies. What nation have we fought since then that has had a populace back their legitimate and professional government and military? It seems that every conflict since WW2 has been us taking (anti-communist) sides in some internal struggle or otherwise settling the difference between two nations. Remember the gas attacks against Kurds in northern Iraq after the first Gulf War? That insurgence to Saddam's regime was bolstered in part by the historic precident of us siding with one political side of a country as it tried to overthrow the other (or defend itself from being overthrown).
Secondly, as soon as we developed the capability, we nuked our last tenacious enemy. Is that still on the table? The justification (which is pragmatically valid in my opinion) was that invading Japan would have cost more lives than forcing a nuclear surrender. Would the same be true of any other conflict in which we fought a genuinely threatening enemy? Our vast armament plays a strong influence in disarming us, I believe.
"Winning" is not up to us, I believe. We can't topple something that doesn't take shape. We can kill and capture every insurgent we find, but we can't stop people from becoming insurgents. I don't think toppling the government of Iran will help us out either. I think a careful analysis is needed of how Japan and half of Germany transitioned from nightmarish military juggernaughts completely at war with us into some of our strongest allies on all fronts.