Well, there are some things in the current balance which are dubious and might be considered to be imbalanced... But securities' MP5 is definitely not one of them. So, you want to leave one of the most important classes only with M4 and Sawnoffs, without a DB weapon? Or you didn't bother to suggest anything else for them in return for the "overpowered" MP5? Newbies have hard time being securities anyways, and you want to make them twice as weak.
There are plently of options to counter this weapon. Sorry, but it is rather pathetic to make such topic after being annoyingly killed a couple of times with MP5. -1.