I largely agree with your assessment. The only out I see is that Russia & the UK can hold out a little bit longer solo against Germany & Italy than the Pacific powers will against Japan, especially if you hit Italy hard from the get-go, so I recommend going almost all Pacific. If you get a G1 attack on Russia, chances are you will have more UK ships than usual which will also help in that theatre. Initially I started favoring going 100% Pacific buys every round based on my own experiences and watching the Allies win in league games. However, I’m starting to think that you need at least 1 round of a full Atlantic buy early on. So my plans now are switching to doing a full round of DDs and Subs the first time the US gets its full wartime income, with all of it going into the Atlantic. A fleet of this size that comes early should be able to prevent Italy from ever building up once you slip it into the Med, which will allow the Western Allies to hold out a little longer while the US focuses on Japan. In this scenario you have to make sure that you hold on to Gibraltar so that your advance isn’t blocked into the Med, which may mean buying a TT or two if you don’t have enough survivors from the early rounds to get it protected before your fleet arrives. The effort Germany and Italy will have to spend to stop your fleet from reaching SZ97 is going to take a lot of pressure off of Moscow & Cairo.
I should also note that the 2 Carrier buy on US1 seems highly recommended (1 Pacific, 1 Atlantic). With a fully loaded CV, CA, plus around 4 DDs and 6 Subs (lots of possible combos, and you have an even bigger fleet if your entry was delayed significantly), you can smash almost any fleet the Axis can put together in the first few turns, unless they go with heavy naval buys that will give Russia a breather. You can certainly scare off any German fleets that might be trying to cover Gibraltar or convoy the UK.
With 100% Pacific buys you can largely take Japan out of the game by turns 5 - 7, depending on when you went to war and if you were presented an opportunity to smash Japan’s fleet. Once the USA can knock out the bulk of Japan’s Navy and Air Force, at that point the other Pacific powers will have enough income to keep Japan contained while the US shifts to 100% Europe. If Japan is smart and avoids these decisive battles, then the game will run a lot longer and it is hard to predict in advance what your best moves will then be.