Nerfs were expected to come with Season 4.

Season 4 is now live, but some players are complaining about certain weapons in the game. More specifically, the Grau, MP5, and the M4. Rumours suggested that stealth-nerfs were coming the latest update, but they haven’t.
None of the weapons have received nerfs in Season 4, resulting in payers complaining on Twitter for the most OP guns to receive a downgrade to remove the imbalance.
The latest patch notes mention nothing about nerfs in either Warzone or Modern Warfare. Leaving the meta remaining the same, and players aren’t happy.
Some players are even threatening (albeit jokingly) to head back to Fortnite over the issue, while others complaining that gunplay feels stale with most players using the same loadout.
Despite this controversy, Season 4 is off to a solid start. Most players have reacted positively to what season 4 has to offer, including the 3 new in-game modes in Warzone; Jailbreak, Fire Sale and Supply Chopper.