You mention the inferior weapons and lack of fighting experience of the Chinese as a factor of their performance. However, remember that China and Japan had been fighting since 1931, when Japan invaded and occupied NW China. So it wasn't a lack of experienced soldiers. It was a question of bad politics and administration that wasted the experience of those veterans.
Well, fighting long wars is actually extremely devastating for a military force's experience when you are on the loosing side. Just look at the state of the German and Japanese militaries in 1941 compared to 1945.
Wars are won as much, if not more, by the preparations and training before battle as it is by the performance on the field of battle.
Your troops learn the vast majority of their skills in training, and combat experience is as much about overcoming mental barriers as it is about learning additional skills. Although even that may be less relevant these days.
A US study showed that only 15-20% of American soldiers discharged their weapons in combat during WWII. Incorporating psychology tricks to overcome this instinctive aversion to killing other humans has raised that figure to about 55% in Korea, 90% in Vietnam, and probably higher still in Iraq and Afghanistan. This is almost certainly to be one of the causes of increase psychological disorders in veterans, but I am getting sidetracked.
The point is that real combat only adds a limited amount to the knowledge of a soldier, since military planners and leaders normally try to incorporate as much of the lessons learned in past wars in standard infantry training as possible anyways.
What really degrades a military force is continuous, high intensity, high casualty combat over a long period, as more and more of the soldiers who had the most training pre-war will inevitably be lost through attrition, to be replaced by greenhorns with far less training because they would likely have been rushed through basic because of the manpower demands of the war.
A long period of war is also especially debilitating for a military force that is not self reliant on arms and imports much of it's best weapons as China did in the 30s, because it becomes increasingly difficult and unlikely that advanced weapons would be easily and timely replaced because they had to be imported. So inferior alternatives had to be found, which would further degrade the fighting capabilities of the military.
A lot of painful lessons were learnt during the Anti-Japanese War, and many of them continue to shape and influence PLA policy today, like China's absolute insistence on self-reliance of all mainstream weapons systems - the PLA would never want to be in the position of the Nationalists whereby the equipment lost during the first engagements of the war were actually the best equipment they ever had with only inferior replacements readily available for the rest of the war.
But I think we are really starting to get sidetracked here.