Supply hain logistics is the flaw in the Big Gulp.
You can;t keep a filled supplt line protected all across the Pacific. And to build up for that one decisive battle, you are going to lose your initial wave of TRNs doing it.
So… you take a few turns, you build up your fleet, and then after 3-5 turns of pure US PAcific Naval builds, you sink the Japan fleet.
NOW you can start to build replacement TRN’s (1 turn) and sail them across the Pacific (2 more turns) to have an impact. Try to add the TRNs in the rear areas before the fleet is gone, and they get SUNK before they get past Pearl.
No matter how you slice it, Japan has AT LEAST 6 turns before the US can bring their might to bear in any meaningful way. And with just 1 new IC and 3 new TRNs, Japan is dropping 11 units a turn into Asia from J3 forward (2 in J1 w/ 1 TRN; 9 in J2 with 3 at IC, 6 via TRN; 11 J3+ after teh 4th TRN is built in J2), so call it 55 NEW divisions, plus 7 to start…
SIXTY TWO DIVISIONS
Even with all INF, that is still a heack of an issue for Russia that will have produced only 40-50 new divisions in 6 turns… and has German as well as Japan forces to deal with.