[I count as main faction only japan and german because whe cant know if italy get his own tree for now]
Thinking about it japanese infantry tech tree is very small leaving aside veichle one whe already get almost all japanese infantry equipment of the ww2,Whe miss only something like the late war type100, full auto mauser c96 and some other infantry mg but for who have grinded the initial 26 level he already have everything he need
So for make it more bigger i think developers need add some german gun in the japanese tree and in return some japanese gun in german tree
Something like this
-
normal mp28/mp34 in japanese tree and s1-100,mp28 (50rd) and sig bergam (mp34 50rd) arrive in german tree
-
japanese get kar98k,carcano,normal zk29 and the normal zb the german get the Japanese zb scoped
-
both side get the full auto c96
Nothing to harsh or ahistorical mostly is sharing similiar gun for inflate both progression and make it more completed