Okay, so I'm friends with a military history nerd who says that Japan's tanks were pretty awful during ww2, and that their doctrine for them was really dumb, treating them basically as infantry that required fuel. He claims that had Japan put more effort into tanks, they might have been able to win in China, and possibly win the war.
However, I really don't see how that could work. While China has a lot of nice flat tank country, the main enemy the Japanese faced there (as far as I know, at least) was their own supply lines, as China's awful infrastructure prevented them from expanding any further than they did in real life. I can't imagine adding large amounts of fuel on the list of things the Japanese needed to lug out to the middle of nowhere would help their supply chain any.
Meanwhile, in Burma, not only was the supply situation awful because like, dirt roads in a jungle aren't really good for that kind of thing, but like, they were in a jungle, which is basically the exact opposite of good tank country. Even if they had been able to supply large amount of tanks out there, I can't see what good they'd've done.
Meanwhile in the pacific islands, the supply situation was a lot less awful because you really couldn't get that far away from a port, I still can't see what good tanks would be. Like, from what I understand the optimal use of tanks, at least back then, was to break through enemy lines so you could encircle and destroy massive enemy armies with a numerically inferior force. But like, the pacific islands they fought on are, as far as I know, pretty small. Is there even enough room there for that kind of a maneuver there?
At the start of the war Japan had a a tank doctrine based on infantry support. Tanks would support the infantry to take strongpoints as mobile fire support. After reviewing the German invasions of the early part of the war, the Japanese changed their doctrine so that tanks were the main force and infantry and artillery supported the tanks. After early early actions against tanks the Japanese realised that their vehicles were not suited to tank-on tank warfare. This led the Japanese to install heavier guns to an extent, but later tanks with 75mm guns were kept on the Home Islands in preparation for the expected invasion. The Japanese had a great deal of experience with tanks and did have some success against allied tanks, but this was countered by the increasing obsolescence of the vehicles. When the war began much of the armoured force was dispersed to pacific islands which varied greatly in terrain and conditions. In many cases these tanks were dug in to act in a defensive manner, and conceal them from enemy aircraft and naval gunfire. On the larger islands, tanks would be tasked to charge the enemy forces from concealed positions. The practice that the Japanese developed of waiting for the enemy to land before engaging, often meant that US M4 tanks and anti tank guns had already come ashore. Japanese Tank divisions in a defensive role often lacked infantry, as the divisions were divided into battlegroups, this degraded their combat capability. Japanese tanks, while having thin welded and riveted armour, were well built, small, light and medium tanks which were quite suitable to operations over, crude roads and waterlogged areas, however they were still very vulnerable. The Japanese did improve their vehicles and doctrine over time, but these were often secondary to larger improvements in other areas of the military.
If the Japanese had not neglected their tank design and doctrine approach would the Japanese armoured force have been more successful? Would your friend be right in saying that "... had Japan put more effort into tanks, they might have been able to win in China, and possibly win the war."? I argue no. The armoured force would still be subject to the overall strategic conditions which dictated that the size of the tank forces would be small. It would still be operating on unsuitable terrain at the end of long and vulnerable supply chains. A victory in China or Burma against the allies, could not be won by an improved tank force alone, even after early successes, due to the nature and conditions of the of war being fought. Operations in the Pacific Islands did not see the use of tanks as a decisive weapon. It is most likely that an improved tank force would not have expanded any early existing successes that the Japanese had, nor would it have prevented any defeats suffered by the Japanese on land, when the broader war situation turned against them. Diverting resources to improve tank production would have drained resources from other programs, and complicated existing supply lines and deployments. For Japan, the war was focussed on the war at sea and in the air, which dictate the success of the land operations. Improvements to the armoured force would not have made a difference to defeats in these areas.
To address your other queries: The main enemy in China was the Allies: the Chinese, US, British and Soviets. China very effectively used guerrilla tactics in occupied areas. In Burma as in the other early theatres, the early battles employing tanks were highly successful for the Japanese, despite tank losses. Later in the war issues with supply among other things, began to cause exhaustion and disease amongst the Japanese. Tanks were used by both sides in this campaign. Pacific islands began to prove difficult to supply for the Japanese, as transports could be interdicted and islands cut off by US submarine operations, or bypassed altogether.
Sources: Asiatic Land Battles: Expansion of Japan in Asia. By Trevor Nevitt Dupuy. Asiatic Land Battles: Allied Victories in China and Burma. By Trevor Nevitt Dupuy. World War 2 Japanese Tank Tactics. By Rottman and Takikawa. M4 Sherman vs Type 97 Chi-Ha. by Steven J Zaloga.