I don't see people have to justify their use of the MP40. I use it because it's the best gun to use, no point giving my self a disadvantage from the start just because it's for "noobs". The gun is good, it's accurate, has a decent range and can drop people quickly, now while it isn't supposed to be as powerful as it is, Treyarch haven't done anything about it so you can assume that maybe they did mean to make it that powerful or maybe it just isn't that damn important.