How do I justify anything but Russian infantry?
Because when I play Russia, I do not want to sit back and wait for death.
Let’s say you only built infantry, and have a fat infantry stack on West Russia. OK, I have German infantry and tanks that I push to Ukraine. Sadly, your infantry stack has very little attack power, so you have to retreat to Caucasus instead of being able to kill my Ukraine stack. Next turn, I take Karelia, West Russia, and Belorussia, then I proceed to start grabbing Archangel and West Russia. Now Russia’s income is lower, and Germany’s income is higher, so Russia can produce less infantry, and Germany can produce more tanks.
Then Japan comes in from the east, and Russia is forced to retreat to Moscow. Caucasus is abandoned, and that’s usually the beginning of the end.
Probably UK and US have some tricks to play, but if Russia starts losing IPCs early while Germany gains them, it’s not good for the Allies.
Suppose Russia just bought a few artillery. Suddenly, it’s attack power jumps, and Germany has to think twice about leaving its valuable tanks where they can be destroyed. So Germany has to stay back. Russia can get more IPCs, which it can use to continue to produce more offensive units instead of just infantry; Russia can use those IPCs to continue to create offensive units to keep Germany and Japan back.