It did make it clear that attacking Amur even when not defended is a wrong move. Normally UK1 declaring war on Japan is a godsend as you can take their islands without any USA interference in Europe. There is no situation the fleet is really neede (fully) in SZ6.
What about sending two full transports with carrier, battleship etc to reinforce Kwangsi. Losing Yunnan is indeed terrible for Japan. This provides enough threat for the UK to remain silent, provides force to take over islands or can simply fight against the Chinese in Yunnan.
Does not need JDOW1 to help Europe while also not weakening Russian border that much. Might be better for Japan to wait a couple of turns with Russia if Amur is not stacked and just focus China then while prepares for India/Sydney Crush.
Yes they do not gain much IPC but with China defeated in 3 Turns but you actually save a lot of IPC that needs to be spend on ground forces fighting Chinese otherwise
I come to think that a actually the United Kingdom are the game makers for the Allies if given the chance, the ones who delay delay and will take every opportunity given to this from the first turn. Especially for Italy in all games but as shown also possible for Japan or Germany. So they need to be threatened, contained or quickly decimated. Germany going Sea Lion is sub-optimal, Japan going India is optimal. I have been through a lot of battles in the League section and the UK making 35-40 early on dis not seem an exception.
Therefore I think the best Axis early investments are in threatening the UK (transports) and placing them able to force UK into defense instead of offense. This gives the Axis the power do the offense in the first few turns while all Allies are forced into defense.
Better still, because of these early UK investments you can focus 100% on Russia or the USA later on, instead of reacting to the UK.
This theory of UK first goes will with the Afrika Korps strategy, as Africa and Middle East are the UK stronghold and money maker. Without it they are a minor Ally, with it a major Ally. When Italy is making 40+ IPC (possible when Axis go UK first) it is able to defend its own + Europe against the USA. Making it possible to fully focus on Russia and win the game.