The thing is that Japan's infantry is better early on i think. So its hard for China to fight them. But AI can do it also as i showed above.
Also for players those infantry can be hard to fight. But they are not supermen. With Britain i could defeat those Japanese infantry after some time, when i could set up some nice divisions.
That takes time though, because of earning army xp, producing the necessary artillery needed for high soft attack value, and having it all set up for maximum infantry punch, like assigning infantry experts in government and such. But early in game, maybe its impossible to beat them?