Well the MP-5 is decent for what it does. The police and special teams use it and still use it. Then again they tend to have a very specific mission like hostage rescue and similiar surgical strikes where they do not have to have a weapon that is broader in its use. And of course police are getting more and more apropriate weapons like a version of an MP-5 whatever its called in 40 S&W and .45 ACP and 10mm which are even better as they have greater stopping power and less penetration <save the 10mm> which is even more ideal for police operations.
This discussion even has me toying with the idea of a character who hefts an MP-5 as his primary weapon, its a sturdy system as long as you use it within its limits. I mean in an urban enviroment, or dense woods or similiar then I'd love one. In the open plains well I would just have to stay out of everyones range
I would think, the MP-5 for those nations who used it as a primary arm, it was issued more on par with a Carbine than a full sized battle rifle. Remember, those nations who used the MP on a large scale got the shaft when the US forced 7.62 Nato, and then after a short time we switched to 5.56. Alot of the European nations had invested in a 7.62 System mainly the G3 or the FN or a variant. And sometimes a full sized battle rifle is to much but a pistol just ins't enough. And thus, the SMG was issued. As I said similiar to the US and how we issue carbines.