Alpha 3 is an evolution of what originally started as a setup change to address imbalances in the Pac1940 game.
The original setup change addressed Pac 40 only, and was called Alpha, and was meant to be used in Pac alone as well as Global. Imbalances noted in Global began to influence the alpha revisions, going from Alpha, Alpha +, Alpha + 2, etc. As these changes were made to address global, there was still a desire to use these modifications for the theater specific games, but this was not a playtesting priority (most people has transitioned to Global only as their primary game - alpha began before Europe 1940 was released). As the theater games became less of a playtesting priority, the national objectives were revised, and this is probably the primary driver of theater imbalances at this point (particularly US objectives in the pacific theater & Russian objectives in Europe theater).
I would recommend using the Alpha 3 setup and rule changes. I would recommend using OOB national objectives until official objectives that apply to the theater games are released. Alternatively, use national objectives from Alpha 3 for all countries but US (use OOB for those) in theater specific games.
The one hanging option that’s been noted many times for the Europe theater is that the Siberian reinforcements should be abandoned and instead Russia ALWAYS collects 9 additional IPCs each turn that represent the eastern provinces not shown in the Europe theater.