I agree - I never meant to say that the US should be more powerful in the game. More important than historical accuracy is the creation of an interesting and fun game to play. It would not be any fun if all that was required was that the US concentrate its forces and industrial might to squash Japan in every game. There has to be a chance for the Japanese to win, otherwise why go through with playing the game?
Incidentally, the number of US destroyers for December 1941 already excludes the 50 destroyers transferred to the Commonwealth in the September 1940 Destroyers for bases agreement.
ETA: Imperious Leader also has a good point about quality. The Japanese battleships, aircraft carriers and air wings, and destroyers all had significant quality advantages over their American counterparts shown in battles throughout 1941 and into 1942. Naval battles are a little unpredictable, though, so there are lots of factors involved.
On an unrelated topic, I could easily find Royal Navy numbers for 1939, but if anyone happens upon RN strength in Dec. 1941, let me know, just for the sake of a contemporaneous comparison.