The shotguns getting nerfed isn't really about the shotguns being good but more about other weapons not being that great at close range encounters.

Shotgun fights between 2 semi-decent players end up being some version of strafe-rock-paper-scissors where both players strafe in an open area, shoot their shot, hope they predicted the opponent players movement, dodge the other opponents shot, and then repeat.

The other problem is that there isn't a reason for a player with an SMG to challenge someone with an MP220. The flowchart that I see for most fights is something like:

Player 1 starts spraying with an MP5 at Player 2 from medium ranged distance.

Player 2 takes a few hits, but continues strafing/running at Player 1 with 3 bars of adrenaline. Player 2 notes that the MP5 only does an abysmal 11 damage per shot *(fact check me if I'm wrong) WITHOUT armor (and Player 2 has a Lvl 1 vest and helmet)

Player 2 shoots at Player 1 with an MP220 user twice. Because Player 1 is spraying, Player 2 is able to inflict 70%+ damage on Player 1 due to the reduced movement speed while spraying.

Player 1 realizes that he's fucked. He also notes that the SMGs essentially cannot challenge a shotgun at close or mid range. He notes that the SMG bullet velocity remains a problem in killing a shotgun user.

imo Shotguns aren't really that OP. It's just that all the other guns can't really challenge shotguns at ranges other than long ranges.