I have seen people say (not tested myself) that if sealion is in the air, then the “antidote” is to kill japan first.
reason is that ussr will be able to get a very strong income for a few turns, so they will take longer to crush, therefor the 18 infs in far east are not needed against germany and can be used to attack japan. if us goes more or less 100 % pacific, they should be able to crush japan fairly fast (US + UK india +ANZAK + USSR +china attacking). the idea is that japan will fall before russia will, so one can turn around and send everything to europe when japan is no threat.
one thing i consider important to say about fleets, esspecially US fleet is that offensive units are the units for when you are on the defensive, while defensive units are for when you are on the offensive.
example; if you want to defend hawaii, but not go any futher, the cheapest way to defend hawaii (by way of fleet), is to buy bombers and subs. the subs can sit on the west coast, and if japan takes hawaii, you can use them to sink whatever he sends there, ( careful that he cannot block ).
if however you want to advance your fleet/stack, to take new land, you need to make sure that your opponent simply doesn’t just kill your fleet/stack, you only need firepower when there is a chokepoint.
defensive units (like inf) are only really defensive when you plan to put them a place where your opponent cannot simply ignore them and walk around. they only really get to be defensive when you plan to hold something against direct assault. (like E/W germany.