The idea that the Japanese were going to surrender anyway and dropping the A-bombs was intended as a warning to the Russians gained popularity during the anti-war 1970s.
It's proponents pretty much all have one thing in common - they didn't live through it. Those who were actually part of what happened in 1945 pretty much dismissed the whole concept out of hand.
Not only were the Japanese not "surrendering for weeks", they were fighting with ever increasing resolve as the Allies closed in on the home islands. After the Emperor announced his intent to surrender, there was an attempted 'palace coup' by some of the war lords who were intent on continuing the fight.
You see, I've spent more than a little time studying this particular aspect of USA history. My dad fought the Japanese in the Pacific during the war, including Guadalcanal (Purple Heart) and the Philippines. At the time they dropped the bomb on Hiroshima, he was a Lieutenant training for the initial landings on the Japanese home islands - his platoon was going to be part of the second wave of landings. He had been warned to expect 80% casualties, while Japanese losses were expected to be ~10x higher (and precious few Japanese casualties survived).
Dropping the bombs on Nagasaki and Hiroshima may have saved more lives than any other act in WWII.
BTW, back to the original thread topic - I read a book on WWII tanks many years ago (it had lots of neat cutaway illustrations and such - quite an interesting read). IIRC, the reason the Sherman (and other US tanks) had such mediocre guns was that the planners didn't foresee "tank vs. tank" as being the predominate battle tactic. Stopping tanks would be done by "tank destroyers" (relatively fast and lightly armored with big anti-tank guns). It wasn't until well after the US entry into the war that it became obvious that tanks needed to be able to take on other tanks effectively. Further, when the Sherman first showed up in North Africa, it was quite a shock to the Germans - clearly superiour to the Mark III and IV panzers that made up the majority the German tank forces. It wasn't until the Panthers and Tigers started showing up in force that the Sherman was in trouble.
One thing I never understood was, after they came up with the upgunned Firefly Sherman, why didn't they make that the standard kit? Was it due to the availability (or lack there of) of the 17 pounder gun?