I might add, however, that believing a mainland invasion of Japan was necessary may not have been quite so much of a "no-brainer" in 1945. It may just have been standard conventional thinking. After all, they had just done it in Europe, hadn't they? And in a whole series of island battles. So, they were simply following the usual procedure in planning for the next big event. I'd call that a bit unimaginative, but I wouldn't call it a "no-brainer". Not at that time.

I call it a no-brainer NOW, given the benefit of hindsight.