The soviet body armor reduces all damage to the torso by 10%, front and back, at no downside at all for the wearer.
While 10% damage resistance sounds minor, when combined with the Vitality perk, the soldier now often has enough HP to survive an extra shot from an SMG. This comes at no cost besides appearance orders.
There is no reason to use any other kind of soldier uniform because there is no downside to wearing body armor. It is poor game balance to offer an objectively correct choice, there should be trade-offs to consider.
Wearing body armor should either incur a stamina penalty OR a sprint speed penalty (the soldier is wearing a massive slab of metal). Whichever Darkflow deems more appropriate.
Body armor should not be providing damage resistance from the back because the armor literally does not cover the back.
What balancing? German SMGs are objectively worse than Soviet and Allied counterparts (M1A1 Thompson with 600 rpm and 6.8 damage and the Uragan with 750 rpm and 5.7 damage on BR II compared to M38/42 Beretta which is unlocked in Tier IV with 550 rpm and 5.7 damage).
If anything, at this rate, it’s the Germans that need the body armour, not the Soviets. While I don’t agree with removing all benefits (someone paid gold or appearance orders for the armour), having drawbacks such as BAR type sprint speed and shorter jumps and shorter stamina and longer regeneration are genuine balancing suggestions that may dissuade some people from using the armour.
If you mean the Mkb42 G, a self-loading rifle in 7.92 mauser with a detachable magazine for a German version of the SVT-38, then that is a fantastic idea!
If you mean the Mkb42 assault rifles, well, that would cause everybody to demand the VG1-5 to be downtiered and result in a whole bunch of power creep