Id on’t think that DDay is a greater threat than it was before…
Best strategy was (and is) to kill off any transports built by UK each turn.
More dangerous is an attack on Norway - each time Uk got an foothold in northern Europe Germany was crushed soon after - despite German sucesses in Africa…
Also IGNORING Japan is the downfall for the Allies - If Japan does not have to worry about the US island hopping they have free reign in the Pacific and are able to sweep through Asia
More often than not Axis troops linked up in Persia then whittling away Russia - if Japan has enough units to attack russia (Moscow) in force Germany can build enough planes to constantly harass shipping in the Atlantic…
I got used to split forces to cover each theatre, because ignoring one speels doom (no matter what side I play…)
but that are only my experiences ;)
BTW - Sometimes we play Russo-Japanese peach treaty (Russia can only attack Japan if Germany is gone/japan can only attack russia if UKor US capital is gone - though then the game is quite over ;)) - Any hint that Triple A also has a similar rule? (Historical gamer speaking here ;))