Every time I use the UMP I just realize more and more how stupidly unfair it is. The gun has no bad perk setup, no recoil, a huge clip, 3 shots at most to kill, and 2 shots close range with SP. I don't see why you would use any other gun in the first place besides maybe a Famas.
It's not really fun. When you have everything unlocked in the game, you give up doing everything it takes to win and realize that shenanigans really make this game what it is. Playing ninja with Cold Blooded Pro, having the ability to spin around in circles and get incredible kills with a sniper, having a Riot Shield and means of killing teammates in core. Things that no other games can offer.
The MPs (MP5, MP40, UMP) have dominated the CoD series and few things were able to combat these subs. They tried making low damage, high RoF guns to offset the power of these, but it never worked. The sheer damage output of these guns put them in a league of their own and it caused hundreds, maybe thousands of players to ragequit.
This divided the community. The "****ing tryhards with the UMP" and everyone that played casually. I often get complaints by rushers saying I hardscope and that I'm a scrub. One guy even went as far to say that I shouldn't use equipment or Akimbo Rangers. I stunned him because I knew he was in a corner, and instead of taking him on with my MG4 at close range, I dived around the corner and got him with the Rangers. During the killcam and postgame lobby, all he did was call me a bad kid and say the stupidest things. I finally muted him when I realized that I could hear his silenced UMP. He killed me a previous round and the guy had Lightweight which is just so rage inducing. The guy ended up playing with no party. Level 70, tenth prestige, challenge lobby kid trying his heart out to win in a public Search game with nobody to give him props for going ****ing 7-0-6.
tl;dr, the UMP is bad and don't use it if you don't need to.