Sorry, but I just don’t think that Japan and Germany would have taken an indefinite number of nuclear strikes.
I understand that viewpoint, but on June 6th, 1944, there were no nuclear weapons to use, and we did not even have a functioning nuclear weapon to test until over an entire year later (July 16, 1945)
On D-Day, we had no idea if those nuclear weapons we were trying to develop were even going to work. We had a lot of concerns regarding what to expect when it did go off. Out at Los Alamos, there were nervous discussions about setting off a chain reaction through the entire atmosphere. They eventually decided it would not happen, but people DID seriously discuss it. The point is, we had no idea. At 05:29:45 Mountain Time on 7/16/1945, they could have pushed the button, and then all stood there looking stupidly at each other when nothing happened.
Given what we know now, sure...there would have been no need to go into Normandy...or Iwo Jima...or Okinawa. Heck, we could have just said right after Pearl Harbor: “Okay, Japan, you just wait. We are going to clean your clock in the late summer of 1945...”
You can only fight with the resources you have at the time you are required to fight. If we had the B-29 earlier in the war in the European theatre...if we had better tanks...if we had the Iowa class battleships at Savo Island...and so on.