I think this is a perfectly reasonable strategy – but keep in mind that you are forfeiting two victory cities as the Axis. The Chinese can attack and occupy Kwangtung, so you’re losing out on both Shanghai and Hong Kong. This makes it very hard for the Axis to get a majority of the victory cities. Even if you completely crush Russia, that only gets you to 9 VC:
Tokyo, Manila, Moscow, Stalingrad, Leningrad, Warsaw, Berlin, Rome, Paris.
So then you also have to pick up India (challenging without any factories in China), or Australia (hard to hold if you’re mostly going after Russia), or Honolulu (ditto).
The Japanese share of Russian income is just not that large – dripping wet, you’ve got Buryatia, SFE, Stanovoj, Yakut, Evenki, Urals, Novosibirsk, Kazakh, and Stalingrad (15 IPCs total).
Meanwhile, the Japanese income for all of China is Manchuria, Kiangsu, Suiyuan, Ningxia, Chinghai, Sikang, Hupeh, Fukien, Yunnan, Kwangtung, and the NO (18 IPCs total).
So, yeah, given that Russia is a more important target than China, you can see where it would be worth a few bucks to go after Russia instead of China, but there are no VCs in Siberia, so that’s the trade-off. If you actually crush Moscow early, then, great, the gambit worked. If not, then you might gain some very minor economic benefits, but you’re likely to stall out and lose on points in the endgame.