To the Chinese, it was clear that the Allies, esp. the USA, would have to defeat the Japanese, regardless of any local outcomes in China. Therefore, it became a matter of course that Mao and Chang were both withholding significant resources for the postwar settling of accounts, vice seeking every opportunity for battle with the JA.
If China was too expansive for the JA to conquer, it was equally so that the JA was too powerful to be defeated by Chinese forces, no matter what the level of US aid, outside of providing the US Sixth and Eighth Armies, plus equivalent air and naval support.
Makes sense for both sides of the Chinese to want to hold onto their strength until Japan was defeated by the US. With that said, were US military leaders such as General Stillwell aware that the KMT wanted to reserve strength when making criticism of Chang Kai-shek?
Maybe there were some US military leaders saw it better for KMT to be as ready as possible to fight the Chinese communists. Or maybe US military leaders underestimated the strength of the communists and just wanted KMT to apply as much pressure as possible on Japan so that Japan would fall faster and with perhaps a little less pain from US forces.
Stillwell kept trying to get CKS to move on the Japanese and was so insistent on it that CKS forced the recall of Stillwell. The funny thing is that "Vinegar Joe" go on very well with both Marshall and Big Mac. Marshall thought the world of Stillwell and would have given him the Morocco invasion if FDR hadn't sent Stillwell to China. MacArthur gave him Tenth Army for the projected 1946 Japan invasion.
From some quick browsing, Stillwell seemed to have been short on resources during the CBI campaign. That might have made him more pressing on CKS. So I guess Stillwell would have been reinforcing the invasion of Tokyo. On mention of the invasion, while not significant by any means really to the outcome, but, while all sorts of bombing happened, it's said that tank production continued all the way until the end of the war. Of course material shortages and such were still prevalent but production of the Chi-To tank by Mitsubishi was planned to start in August 1945. Plans were of at most to have 170 produced by Mitsubishi and 30 by Kobe Steel throughout 1945. Although the cannon is said to have been the biggest bottleneck for production.