Putting a MIC in china in J1/2 or even J3 is a viable strategy. It makes reinforcements on the continent much easier. You can build an MIC in Korea, Manchuria, Shantung or Kiangsu at the start of the game. Nevertheless, the most build complex is in French Indochina I would assume, but it must be conquered first by Japan.
Building Tanks on the continent obviously gives Japan more punch than building infantry. Nevertheless you should also consider the cost benefit ratio. Infantry is just half the cost, and as long as japan has superior air power available against china the infantry will also do the job. Also consider that in a typical attack with one ground unit plus air force against a chinese infantry you will lose your ground unit 1/3 of the time, and in many occasions even if it survives it will be threatened by a counter attack. Now, consider again, if you want that unit to be a tank or an infantry.
In the end it is always situational. Tanks on the mainland can be quite strong, but most of the time infantry will do the job. If you need fast movers, also mechanized can be a good alternative.
Just my 10 cents.