It's awesome
But They had a very weak tanks in WW2. so I think, You need set them weaker and cheaper.
1 Sherman VS 3 Chi-Ha
It will fun better
Well their tanks weren't so bad that they couldn't pierce the rear of shermans. You have to consider the game mechanics and shermans and T34s are aready cheap. Having 10 Chi-Has roaming around gets a bit hard to control. It is supposed to be a bit similiar to the P4 vs allied armor balance where they will lose decisevely from the front, but can even the balance if attacking from the rear. I kind of estimated with most the stats, but the Chi-ha should deflect often against medium other medium tanks front armor. You also want to make sure they can do a little something to heavy armor to make it fair.
As for the Chi-Nu, they were designed to go head to head with the current medium armor at the time, but like the other medium tanks fail when faced with heavely armored tanks.
The thin armor is also a big weakness as even light tanks can reliably pen them, but they should have a high rate of fire to compensate a bit. Remember this tank isn't about what tank can beat what tank, but rather about how you use the advantages of those tanks. Two T34s will lose easily to a tiger from the front, but is they use their speed to flank they can take it out quickly.
I really don't know why people on this forum try to simplify these discussions down to what tank can beat what. Just because the IS-2 has a lot of armor and lots of penetration doesn't mean a Chi-nu can never damage it. They just need to attack the rear.