To me, the point of a Japan landing in Alaska is to disrupt an American player who is cutting a perfectly optimal transport shuck. That is, if they have 4 transports they only have 8 units to transport.
To me, that style of American play is very unwise. It does not allow for replacement units or for distractions. It also does not allow for you to change what you want to ship to Euro-Asia. You only have 8 units! Whatever you happen to have, has to be shipped! If you had 10 units, you could mix it up on the fly if you needed too!
As for a “waste” I don’t think it is a waste at all. You’ll still use those forces, you just happen to have them earlier then later. That means you sink the German fleet in the Med and lost 90% of your aircraft in return. Well, you have 24 units in W. Canada, 8 units in E. Canada, 4X4 transports. That means you can rebuild 70% of your aircraft this turn without interruption. (Pulling numbers from no where to make a demonstration, not advocating 4X the amount of units you need sitting around with America. 2X maybe. 1.5X is my standard usually.)