What you see on paper, if you're a general on the allied side, where you see these units that look like they should be able to put up a good fight has very little connection to what's actually on the ground. The first islands will be invaded almost simultaneously with the pearl harbor attacks. And then the japanese will have landings in at one one this week. Another week you'll have another. I mean, you can't even keep track of all the landings they do.
Japan's rising sun goes supernova and engulfs a huge area of Asia and the Pacific. A war without mercy begins to develop infusing the whole conflict with a savage vibe.