Black Ops Cold War MP5 was already nerfed after fans complained about how strong the weapon was on launch. Black Ops Cold War clearly had a gun that was superior to the rest of them in the early days of the game, and it was the MP5. We all knew this was coming when entire lobbies were running around with the MP5.
Treyarch announced on Twitter that they were reducing the effective damage range on the MP5 by 33% and adjusted the initial recoil for the Submachine gun Alpha. This doesn't make the gun 'useless' by any means, but does bring it back down to earth.
Black Ops Cold War MP5 Nerf: SMG Nerfed Already
The issue that we saw with the MP5 was that there were no issues. You could effectively take out enemies at close range or distance with the submachine gun. It had a high fire rate and great damage per second. This update makes it more difficult to 'delete' enemies at range, and changes the MP5 from an assault rifle/SMG to an SMG. Although upsetting those that were shredding through lobbies with the gun, it was a fair nerf.
This was an emergency update by Treyarch. Any other updates to weapons shouldn't be expected for until a later date.