Why are the cannons so weak on the 109-E, yet so strong on the Russian planes?

[Soviet Ace]

So I did some research on the topic last night, and came up with basically what TRC found, but I looked up what the German FF cannon (which should be what the 109E in BoP is armed with), had. Here's what I found.

+ Weight : 26.3 kg
+ Length : 1.37 m
+ Muzzle Velocity : 600 m/s (MG FF), 585 m/s (FF/M with AP or HE), 700 m/s (MG FF/M with mine shell)
+ Rate of Fire : 520 rpm (MG FF, FF/M with AP or HE), 540 rounds per minute (MG FF/M with mine-shot)
+ Round types: armor piercing (AP), high explosive (HE), incendiary, all with or without tracer; high explosive mine-shot (HE(M)) (only MG FF/M)