It seems lend-lease equipment numbers are lacking, in comparison to historical deliveries. Also, Chinese had quite good German artillery, and not this crap they have in-game. I have also found, that they used their own version of knee mortars, so firepower is probably too low. All that should increase Japanese loses, but I doubt, that will change outcome much.
Recently, I was thinking, about seriously reducing number of Support Devices in Chinese combat units, so they won't use so much supply. Consider, that their logistics is placed in all those HQs, and Corps are made mostly from frontline troops. But that shouldn't make much difference in comparison with extra supply generation.
So, the only logical solution would be to reduce initial disablement (increasing Japanese one, wouldn't change much, as they can repair this in two weeks anyway).