14/15 = 0.933333… which when rounded = 1.
In other words, it’s statistically close enough to even to be called equal. However, I do agree, that mathematically 14 =/= 15
As for why do they have to be similar? I believe that was the beginning of the discussion: Russia needs to be able to take and hold ground in this version of the game, not just trade it like in previous versions. I am not personally ascribing too that theory, just stating where it started from.
Personally, I think Russia needs 2/3rds to 3/4ths the tanks Germany has and India/Africa needs twice as many as Italy has. Just my perspective on it. Personally, when it comes to Russia, I am leaning towards:
y(x)=(6 Infantry + 4 Artillery + 2 Armor)k + 3 Fighters + 2 Tactical Bombers
Such that: k is the proportional constant. That is, if you have 12 infantry, then my formula would state you need 8 artillery and 4 armor.
Note: the above assumes a significant portion of the game has elapsed and that Russia has had the cash to get the extra fighter and tactical bomber due to either an early break into eastern Europe or delayed Japanese involvement or whatever.