Lets be honest, if the game would try to represent a historical accurate Japanese army - it would stop advancing at BR2.
So even at BR3 we already see most weapons and vehicles being either super rare prototypes, or even pure fantasy blueprint guns or strange import guns.
Now the devs even want to add BR5 for Japan - which is gonna completely alienate the faction from any believable WW 2 immersion.
Why does it have to be like this?
Are there really no other solutions?
I think Japan deserves better, so I encourage all of you here in the forums for Ideas to fix this issue.
Let me start with some thoughts I recently had,
fist, would we apply asymmetrical balance to the faction, we should address the big obvious first - Japan had almost no tanks, the Ha Go series of vehicles was the exception but it was so small, it could just as well be considered a light armored vehicle. Even the BR3 vehicles are gonna be prototypes, so everything above those is bound to be even worse than that - blueprint fantasy.
So now hear me out - what if - Japan would be the only faction to bring in 3 planes and only 1 tank? There are enough good pilots in this community that would enjoy a faction that is balanced around aircrafts and in the end a US Jumbo tank is only dominating Japan vehicles because of tank vs tank combat. A bigger number of planes in the skies would not only fit the faction perfectly well, it would take care of this issue.
Next thing I had in my mind, I remembered how Red Orchestra - Rising Storm balanced out the Japanese faction - better charge attacks!
In Rising Storm the game balance had found a compromise - the US had M1 Garands, Japan only Arisakas, so Japan exclusively got a special mechanic added to them, if a certain amount of players did Katana or Bayonet charges together, they would get a group charge buff - granting extra survivability, depending on how big the charge was you could survive multiple more hits.
That was actually pretty funny to watch, instead of seing constat pressure on the battlefields you had these weird silent moments where the Japanese would gather together waiting for enough players to prepare - and then all of the sudden all you could hear was this massive shout “BANZAAAAII!!!” and the entire Japanese team charging you, which was pure horror for the US side.
Now I am not saying that this mechanic should be copied, but I give an example that asymmetrical balance is possible to achieve in this regard, especially when we look at extra HP, which already is in the game - looking at you evil evil Soviet exclusive body armor.
A simple damage multiplier for Japanese could be added when charging, or even easier, the Japanese Catana could give moral stat boosts, like faster movement speed, more HP, faster bolt cycling, faster reloads, all you had to do is equipping your soldiers with a Catana and he would get moved into higher Battlerating.
Also Japanese could get special gear at higher battleratings, like gas grenades that work like improved white phosphorus - exclusive to Japan, or impact AT grenades exclusive to Japan, and if all things fail, Squad size could get increased at higher BRs.
All these things can be done, without needing to implement too many crazy prototypes.