The reason for the mass of troops is FIC.
Japan can dump forces into Asia while the US floats across the South Pacific. Japan either comes out and attacks the fleet, pulling their trannies of bridge duty to serve as fodder, or Japan stays put and ferries troops.
If they do the former, then you have taken a LOT of pressure of Russia.
If they do the latter, then the US lands HEAVY in FIC: 10+ divisions of mixed INF/ART/ARM
… behind the Japan front in Asia
And with a piece of property that can be reinforced immediately by UK AF before Japan can counter (maybe even FIGS from Russia itself). Drop an IC…
Allied HARD point in south Asia, with massed fleet heavy on transports, which is a lot of defensive fodder, and a rapid threat to India, Africa, and even Japan itself in a few rounds.
Japan has to take the bait and move out on that fleet, otherwise they get pierced in their underbelly, with no way to remove the spearhead.
Eitherway, it stops the flow against Russia from Japan.
Now if you want to fine tune the specific naval builds… do an AC and FIG with 1 TRN one round, a BB and TRN the next, that is up to you. But the more TRN you have in the mix, the greater the land and IPC threat to Japan.