Make the shotgun a better stopgap.
I've came to realized the shotgun is pretty underpowered right now. They can kill Skulks very well but they do very little to Fades. Since shotguns require the target to be close to deal most damage. And the Fades so far are the most powerful melee attacker in the game. As soon as a Fade blinked his way next to you, you're basically being forced to fight on his term where he's the most powerful. The shotgun no longer has the advatage since the Fade can slash harder and faster than the shotgun can fire.
How I've always viewed the shotguns are that they should be the stopgap weapon for marines before they get the access to tier 2 weapons like the grenade launchers and flamethrowers (both being a bit overpowered right now BTW). And currently if the marines couldn't get the 2nd CC in time before Fade appear it's basically a solid indicator that they're on the slow road to defeat. Though, same goes for the alien who couldn't hold and lock down the CC expansions early, but that is another thread.
My point is, why not make it so that when you right click with the shotgun, you would switch into a tigher barrel choke? Resulting a tighter pattern for your pellets. This means you'd be able to deal fairly decent damage to Fades earlier on in a fight, before they fully close their distance and starts slash spam you. Maybe reduce the rate of fire while in this mode just to keep things balanced.
This would mean that the marines would still have some chance of turning things around even if the aliens manages to put up walls and walls of hydras and whipes in the CC expansions early on. That the marines are forced to fight Fades with their tier 1 weapons.