I think the KMT at the time calculated their contribution just enough so the allies won't lose.
Japan was at the time spending as much as over 70% of their income on the military, whereas the US was just warming up, once Japan lost their momentum the war was already decided.
Chiang did not need to risk his precious assets to kick the Japanese out of China, so he focused his attention on how to consolidate power after the war.
I think that's rather unfair assessment -- grossly so. For example, the force China contribute to the Burma theater are the cream of the forces -- include the only mechanized division in Chinese army. And I mentioned before that China was out of ammo -- and an offensive may use up whatever reserve that was left. Before Burma road re-opened, Chinese army received less than one division worth of weapons, and total amount of ammo China received, even after Burma road reopened, wouldn't last a American division a weak in combat. In this kind of instances, just having forces would force the enemy to spend forces to keep watch -- both KMT and Communists use this strategy. If China actually initiated a big offensive and used up the reserves, the whole defensive line would be weakened, even if the offensive is successful.
As it is -- China still suffered devastating loss in the last Japanese offensive in 1944 -- something like 50% of the remaining war-making industrial capability is lost or damaged during the offensive. If they don't have the reserves, it would have been worse.
China was further weakened by internal politics and possibility of coups. And any of those could initiate a total collapse.
A lot of American criticism is for domestic consumption -- they want something to show for the money they spend. China had to worry about the stability of line and catastrophic collapse. China actually had something to lose, unlike the Americans.
A lot of English language books does not have a good appreciating of Chinese point of few, so you really need to keep that in mind.