Seems inherently broken. Terrible damage, obviously, from shotguns at any medium+ range, so having to play as either shotty character in these missions is terrible, especially if you are attempting to solo.
Definitely reminds me of Battleborne's balancing issues with several of its characters who are designed almost purely for PVP and get destroyed in PVE.
Feels like they need to switch to slug rounds instead of pellets at least, or just switch to heavy revolvers so they have some kind of ranged competency. Atlternatively, they could be tweaked so that they can charge up the shot to tighten the spread and increase distance. With a single weapon only system, it's bound to break.
The ammunition bottleneck is also pretty bad. When going solo it takes way too long to restock on ammo, and when in co-op, you're forced to have to kill a target in melee to get ammo back. This needs to be reworked.