The biggest issue with the SOS is that there's honestly a lack of risk to it, despite it being a one shot long reload.
The scenario is EXTREMELY common: You see a guy just chilling on a column. You know he has the sawn off, so you shoot him a little bit to bait him. What happens is typically he'll come out of cover, YOU ROLL BACK, they fire and immediately roll back as well. The person shooting the SOS has no reason to NOT roll back immediately after firing. If you're in range, you die and they roll back anyway. If they miss, they have a headstart on running away. So this immediately creates a gap since you both rolled away from eachother, and by the time you roadie run over he's already bouncing like a jackass and is likely behind cover again, restarting it. This is so annoying in a 1v1 because they will literally just run away and miss shots, but because of the gap you naturally create avoiding the cone of instant death they get another shot at running away until they reach an area of the map where they have no easy cover to find and you can just down them from back shots.
This is also why I'm alright with the SOS in koth. It's then required to be used offensively, so someone shooting the sawn off, rolling back and running away while I'm in the ring is just giving me more points. When you are defending a point with the sawn off, the reload becomes an actual risk as you really need to now land your shot and avoid other players while trying to get an active. It can become hectic and fun as hell when used like this.
So when you have an entire team doing this camping, run away strategy the main way to fight it is to play extremely dangerously and roll TOWARDS them and pray that you get to their side and they miss the shot.
I think for deathmatch it needs far less ammo. Literally talking one, two shots so you actually need to hit people with the shots.