(a) For political reasons, the Japanese Government did not want to conduct a 'total war' (quite similar to Germany in the first half of the war). Full mobilization of the Japanese manpower and industry did not begin before late 1944. It is quite interesting to notice, that the IJA even stood down one regular infantry division (4th) after the conquest of the SRA.
Wow, really? That surprises me indeed, they stood down an ID? Not that they had so many...
I knew that also IJ was too reluctant in its general war plans, and just as the Germans widely underestimated the scope of what they kicked loose (or how to win it, if at all), but also widely underestimated the degree to which their economy and military could lastly be expanded. Ok, the latter may also have been possible due to the dire need in 44-45, but still. But that they would stand down units while pushing forward in Burma and elsewhere still...
About China: I tend to agree -- it binds a lot of IJ forces, even if you ultimately loose it. And perhaps more importantly it can also be a black supply hole for the IJA, which may help the Allies in other theaters and accelerate the IJ breakdown (esp. with the expanded OOBs outside Scen 1). Silent China sounds like forgoing any advantage, though I never played it.
If any IJ player wanted to force China, it won't hold in this game. Maybe it would have in real life either, just some longer; I don't know. Maybe with stacking limits and higher garrison requirements, but I guess LoBaron had a point that stacking favors the side with "higher quality" units. I am curious to see the Treespiders or LargeSlowTargets mods with added small supply bases and changed infrastructure. Supply should be the main limiting factor for both sides in this region, if that can be mimicked... Else it would be a thought to reduce VPs in this region -- my take would be that the Allies would have kept pushing and maybe even faster if China would have crumbled. It should not contribute to a victory by points much. Though all its destroyed squads and planes will add plenty already.