I think its hard to win if you completely ignore one Axis power to focus on the other. In Revised it was easier to go 100% one direction and race against the clock. In 1942.2 it takes a round or two longer for the Americans to cross the Atlantic, and for the UK to set up on Europe. Russia is weaker too, because of all the German tanks they have to face down, and because their own tanks are more expensive. I think its important for the Western Allies to cover the center of the game board with air. Whether its British fighters and bombers, or American fighters and bombers, either way, its important to hold the line at Caucasus, which invariably brings you into conflict with Japan in KGF, or Germany in KJF. If you have enough air at the center to keep Japanese ships from controlling Suez, or launching fighters out of sz 34, its easier to manage the drop on Europe in KGF without Russia collapsing. Similarly, having air at the center is key to holding the line in KJF, since you need to keep Japan restricted on fleet movement, without giving up the canal zone and the center to G. So in either game, I think you need to at least manage one side, while you focus on the other, completely ignoring one theater for the other, seems more dangerous here than in previous games.
The kind of strategies I see that seem effective, are the ones where Americans push air early into areas of the board where they can cover multiple sea zones or territories at the same time. Bombers are especially effective when used like this, to put the shock/stall on one theater early, and then rapidly move to the other theater where they can concentrate or coordinate for a break out maneuver.
USA is probably the most challenging nation to play, because you have to plan everything a round or two out. This board is somewhat different than the boards that came before it too. Here, in the Atlantic crossing for KGF the US leads and UK follows (whereas before it was the opposite). UK also has to focus more energy in support of India/Russia, which stalls their drops on Europe by several rounds. This makes it harder to just throw everything against Germany, because if you don’t put any pressure on Japan they can race to the center faster than the Allies can. Likewise, in a KJF game, the UK alone doesn’t have a whole lot of options when it comes to propping up Russia or covering Africa.
I think where the Allies run into problems, is if America tries to push out an expeditionary force before they have enough airpower to cover it, or enough air to make the ground units truly effective once they land, or if Allies cede the overall air advantage to Axis at any point. Magnified bomber builds are probably the easiest way to get the USA into the fight across both theaters and start pressing the advantage early. The Americans begin the game with 5 fighters and a bomber. Which means that if you magnify the air purchases over just a couple builds, you could potentially have a massive bomber armada (along with the 5 starting fighters) to close out the third round. Alternatively you could have about a dozen or more fighters. With an air force like that moving towards the center, you can threaten air attacks across a pretty broad area of the gameboard (both on land and at sea) which lends itself somewhat towards a more balanced or dual-theater game.
Its not impossible to make a late game push in two directions at once, if the center is secure, and the Allies are collecting enough IPCs. But you have to set up some kind of logistics train out of USA first. Trying to do something in two theaters at the same time, at the very beginning of the game usually just invites disaster, since you won’t have enough power projection to have much effect in either theater. Axis will see it coming have too much time to build up their defenses.
In the most concentrated bomber build strategy, the Americans could have 7-8 bombers on placement in the third round. You could have potentially 10 bombers on placement by the fourth round! Its hard to overstate how effective an armada of 10 American bombers can be. Combined with the American starting fighters, this air force alone is large enough to destroy basically any fleet that Japan can drop, almost anywhere on the gameboard. Combined with US starting ships it makes it almost impossible for Axis to achieve overall naval superiority in the endgame, and restricts the movement of any fleets they do have so severely, that control of the center becomes much harder for Axis to orchestrate. The magnified attack power of 10 bombers makes it much trickier for Axis to push small stacks of infantry to the front, stalling their forward movement, or ability to trade territories with light infantry. Perhaps just as important, they can rush 10 defense fodder to almost any territory on the board in a flash, saving the day on a critical defense.
And of course, if there are no easy enemy units to destroy, then the 10 bombers could always start bombing Germany back into the stone age, Potentially cutting German production/purchasing power in half, especially during a key round where it might make a difference. 1 or 2 bombers alone can’t really accomplish this, but 7-10 bombers grouped together in a bomber stack, can be crushing. I think if you want to try a balanced theater game, you might consider them as an alternative early game purchase, once you have the clear air advantage, its relatively easy to start dropping transports and pushing ground. Part of this is because Germany will have to stack much deeper on defense, for fear of bombers on amphibious assault.
You can do similar things with fighters, if you magnify the air build that way. Concentrated fighter builds usually take a round longer to set up, and here its helpful to drop them directly onto a carrier deck in sz 56 or 11 so you get the movement advantage on placement, so the cost of setting up is a bit more too. Fighters can also be used to cover Axis fleets, or to defend transport trains on allied carrier decks, but they have the advantage of being able to defend key territories at the center as well. 10 American fighters on Moscow, and becomes very challenging for Axis to bring enough force to take.