MP7 pre-nerfs was a bit OP when it came to actual damage it did, but it had too much recoil, nerf happened to both it's damage and the removal of AP rounds for everything except bolt action rifles and it ended up being more or less forced to always have a 40 round mag unless you wanted 1 or 2 kills per mag in it's current state.
On unarmored targets currently it's more or less perfect, but the second there's armor in the picture it becomes a bit of a regret to have brought in the loadout, exactly the opposite of what the weapon is designed to be in real life. If it's not gonna fit it's purpose-made design, might as well just replace it with a CZ Scorpion Evo 3 A1, or a P90, or even a Kriss Vector (in 10mm to make it a bit easier to balance).
As it's a weapon that at the very most is used by 2 players in a match, it's not really a horribly OP overall presence when everyone else is using the G3 or M14 and dominating lol