MP40's were as good as Sten guns IRL, and as for now Commandos are the highest dps unit in game so Relic can give MP40's similar stats.
MP 40's weren't a common weapon in Africa or even Europe. MP 40's became most wide-spread with the Volksgrenadiers in late 1944 'till the end of the war. Before that, they were only really issued to officers, combat pioneers, various crews, and on occasion select soldiers for assault ops.