Well, Von Mudra, we cannot have the actual rate of fire of 1200 rpm because of engine limitations, so we've got either the option of 2x600 rpm, which would be the correct ROF, but has the downside of not being as effective, as 2 bullets usually have the same effect as 1 bullet (it kills the player), or 1x900 rpm, which would be an incorrect ROF, but makes the gun more effective. Since we feel it's more important for immersion for the gun to be effective, rather than have the (strictly speaking) correct ROF, we have chosen the second option.
The downside is that it's practically identical to the MG34 now, that's true. The only real difference is that it has 250 bullet belts instead of 50 bullet magazines.