It’s not FORCING me to tie up any units. I build extra units every round, by turn 7 I have between 6 and 12 extra ground units anyway. Units I can use to fill transports if I have a bad battle and need to rebuild fleet or air power (which is why I build them. It’s the same as saving 3-5 IPC a turn or more when you don’t need more units, except you build the extra units instead.)
Of course, I could only send 2 units into Alaska and win. Or 6. Or 400. The number of units is irrelevant. What is relevant is that Japan has thrown away 6 IPC worth of equipment for a 2 IPC piece of land and failed to divert a single unit from Europe that couldn’t get there anyway at that time. Nothing is held in reserve by America. Nothing is wasted by America. America just built more units then they could transport anyway because it allows them leeway in the next rounds builds to buy fighters, bombers, transports, submarines, carriers, destroyers, battleships, aa guns, whatever they need to fill a need for that round without adversely effecting the efficiency of their transport trains.
Honestly, I LOVE it when Japan wastes money and resources on Alaska. I have more then enough to thwart any build up there (though I usually wait a round to see if the ID10T will build an IC or try to stack it and hold it) and I have lost nothing from it. 2 IPC worst case scenario, reducing me to 35 IPC or 10 Infantry, 1 Armor which is 3 units more then I need to fill 4 Transports. :)