The fact that the US won may or may not have anything to do with the quality one-on-one of the US infantry. We won largely because we built an overwhelming number of weapons, bombed the hell out of the opponent first, and usually outnumbered him. If you want a more sourced discussion, go to my book "A Patriot's History of the Modern World, vol. 1." I would like to see YOUR history and sources for any analysts of WW II who thought our infantry was superior to the Germans.
Japan is a totally different ballgame, as often it was Marines doing much of the fighting, but even when regular Army, we often were fighting units that were severely undersupplied and/or starving.
I doubt you can read any of my books and call me a "Germanophile," but the research is pretty clear---again, Col. Mansoor notwithstanding. And most admit, as do I, that the primary difference in the armies until late 1944 was training. The Germans had trained in war conditions since 1939 and some of the units were extremely veteran.
You would have been better served reading the actual unit diaries/after-action reports of the units in the theater than "sourcing from scholars". We tend to brutally honest in our reports, so the truth is available to you.
Bottom line, we crushed them - and you would do well to make the acquaintance of a few of our diminishing supply of European theater combat vets. They were awe-inspiring. Look up "Hurtgen Forest" and "Aachen" to gain an appreciation for how damn tough our infantry really was - or just visit one of the many cemeteries in France, Belgium and Germany to seem how many we lost versus how many of them are buried there.
Writers that find some new "truth" about how lousy we were against the Nazis are a dime a dozen lately. You are wrong.