Tell me again how you plan to beat this
with this
How is an army designed around light tanks with a couple inferior medium tanks, supposed to stand up to an army based around excellent medium tanks and some heavy tanks?
Besides, the IJA was heavily into defense and ambushes. Who wants to play against a faction who's main infantry can plant (non-crit) AT mines as a way to make up for their lack of real Tanks? Or gets ambush bonuses for hiding in cover, because that's how the Japanese fought, they ambushed you from the trees and bushes. What about units they spawn out of forests and hedgerows because they had tunnels in there, or they were hiding there all along?
You said "They would be no worse off then the current american faction", but that's not true. They didn't field any equivalent to the M4 Sherman Tank, and they didn't have any equivalent to the M36 Jackson. Imagine if US Armour stopped at the M5 Stuart, and they tried to compensate in other ways?
Insane surprise and versatility bonuses would need to be given to make up for the complete lack of any armour that could go toe-to-toe with what the Soviets or Americans are fielding.
Its just like how the Americans are based around infantry and light armored tank destroyers, Japan would be based around light tanks and infantry with hit and run tactics. Their air force would be their strong point and if they add in naval artillery that would be pretty powerful stuff. Although Italians should be added in first along with the British Commonwealth.