The Russian grenades are fragmentation grenades. Perhaps the pieces should travel farther but they are designed to do damage with schrapnel. The German grenade is designed to have as little fragmentation as possible, instead relying on explosive overpressure to kill, especially effective in small spaces, trenches rooms etc.
I am not sure if the grenades are modelled differently in game, but the Russian grenade seems not to have enough killing power over enough distance. Out doors, the German grenade was far less effective but the Russian should be able to cover about 15 metres with flying pieces of it's shell.