I found out that shotguns (and shotgun users) react very bad to percs, since they completely negate their cover advantage.
But yeah, shotguns are supposed to be good at CQC, so it doesn't make sense to complain about that aspect.
What is worth complaining about is that partial hits are often hard enough to barely 2-shot you, meaning that you take one shot and think you just got grazed, then the second shell comes in and BAM you're dead. Opposite is also true, you think you scratched your opponent, somebody finishes them off, and you find out that you dealt them over 500 damage.
That's very misleading and gives the impression of a luck based weapon, which is infuriating. The pellet mechanic has to be tuned so that damage is more evenly spread, because dealing 80% of your max damage by hitting 50% of your pellets is wrong.
That, and out of range kills.