The Japanese fighting on too many fronts brought their end.
I mean they have not even won in China as it has become a stalemate then they picked a fight with the British and the Americans.
They came close to war with the Soviets but they lost the border conflicts and they got pushed out of Mongolia which led to Japan not to join against the Soviets alongside the Germans.
Japanese taking on the South East was a gamble which paid off. The British got caught off guard. The Americans also got caught off guard in the Philippines.
Japanese were winning but by late 1942 is when the conflict started to turn against them as their enemies did not surrender and come to the table.
That explains why Yamamato did not want to attack the USA when Japan's hands were already full.
The British were in no shape to fight Japan and Japan knew this, which is why they attacked. Neither were the Americans. If you are going to war with the European powers in Asia, it was always going to draw in the Americans. So Japan has no choice but to strike first.
If the British navy has been able to stop the Japanese, then Britain would have won. However the Japanese weren't stopped until Mid-way and the Battle of Coreal Sea. Their logistics were over burdened, even the Americans were struggling with logistics later in the war, so for Japan it was very difficult, they couldn't afford to lose any ships.
So for me the Japanese victory comes from their navy dominance over the Western Pacific and Indian Ocean in that part of the war. The question for me is could the British have defeated Japan on our own, if we weren't at war in Germany. Basically Japan's fleet was so powerful and capable in that part of the war, that they could have defeated the Royal navy regardless of us being at war in Germany.
As for China, that was mainly and land conflict, where much of the Japanese forces were. So you are right if they could have ended the land war and pushed those forces into other places, it would have helped them a lot. They even took Madagascar as well. They in reality the Japanese did far more in the war than the Germans did. However they were just taking over European colonies for the most part. In terms of the US, I think the Japanese did the best they could do. All in all it was a wonderful and brilliant strategic move, much better than Hitlers move in Europe. They knocked out Britian/France/Holland/US for about a year, they took a lot of China and Korea. So the Japanese deserve credit for it in my view, though I do hate the way they treated British prisons and I can't forgive them for that. Against any serious European land power the Japanese would have been defeated in my view.
Now if the British had been able to full re-arm before the war, then Britain in my view could have defeated Japan. We were building 11 carriers. So yeah they Japanese would have struggle with that. It would have been a much more even fight.