the prerogative to advance or not strategically was always with the Japanese
This statement is complete fiction. Advances by anyone to anywhere are 99% a function of how well the troops are supplied. Japan supplied a 20th century army (sort of anyway...they needed more ammo for their breech loaders and gasoline for their tanks) with a 16th century supply establishment. In WitP tank units go racing around Western China apparently "living off the land".
For a wagon the hay/oats/other horse fodder take a much greater percentage of the wagon's load than the gasoline needed by a truck for an equivalent distance does. Railroads are needed to sustain an advance and China relatively few and they didn't really go to places to where the Japanese needed to go to conquer China.
Frankly the Chinese OOB and Japanese OOB are not the problem with the China Theater. The problem in WitP is that there is no differentiation between a the logistical support capabilities of gasoline-powered truck and a hay powered horse-cart.
Yes, to both these statements. They are not inconsistent. A good idea of the nature of the Chinese Theater can be had by a study of the Spanish conflict in the Napoleonic period.
It, too, was theater level for the time. In it, the prerogative to advance or not strategically was always with the French. The French would advance, the Spanish would be defeated, but never catastrophically. They would disperse and then regroup.
The Spanish army had a small core of well trained, professional, units, and it was around these that the "armies" of Estremadura, Aragon, the North, the West, coalesced. Much the same, Chaing had some very well trained, well equiped, and highly motivated units that he kept close to home. He used tham very sparingly, just like the Spanish juntas used their "Royal" cards.
It was a war of space and time and communication, and above all, logistics. The French had over 250,000 troops in Spain, but cound never collect a mobile column of more than 10-15,000 for an op in an area. They strained every resource to collect 50-70,000 troops to confront Wellington's advances and strategigally turned him back on two occasions. Both Wellington and every French commander screamed about the utter inability to supply their troops in such an environment.
Read about is. Understand it. Think of China as Spain. Internally, think of Cuesta, Romana, Blake, Suedes, Rodriguez. Externally, think of Stillwell and the Allied presence in India as Wellington in Portugal. I think you will begin to understand.