Does DOW on J1 or J2 effect neutrality between the Soviets and other Axis powers? If Soviets still have to remain neutral until RD4 do you wait to attack Russia with Germany?
No it doesn’t. Still, Germany should probably declare by G3 and on G2 in some circumstances.
If you’re skeptical about J1/J2, i would recommend trying the standalone Pacific game a few times, trying each of J1/J2/J3. The advantages of an early declaration and early expansion for Japan are pretty apparent in that scenario.
Imho J1 and J2 are also superior to J3 in Global (with 2nd edition rules), but in some exceptional circumstances (Sea Lion with a shot at success) J3 is warranted.
I’m personally a fan of J1 and have plenty of success with it, but my version does NOT include a J1 attack on Pearl Harbor. Instead, at the end of J1, Japan should have 3 fleet groups (one by Japan, another by Borneo, another by Phi) that are poised to seize money islands and other critical targets such as Malaya on J2.