Singleshotter is viable in tb but in rt it is not because he can't deal damage fast enough.
Here's how it can be viable:
Every gun that has singleshot ability can stack singleshots by changing firing mode. When this attack is released, the character fires as many singleshots as he had chosen and has aps to perform. So if you got AR with fast shot, brof and 14 ap you can perform a 7x stack shot that spends all your ap. It will produce 7 ar shots that will impact the enemy in the same way as if they were separate single shots. Calculating crits and damage perks for each shot separately.
This replicates exactly how turn based fight works because if it's your turn, you can fire those 7 single shots at the enemy without him being able to move away.
To prevent the ammo panel becoming too bulky with the stacking attack types, the stack attack should be applied by alt + clicking on the panel when singleshot is selected. It could also be hotkeyed.
Animation would be the character doing the normal firing pose but sound would be the gunsound played rapidly as many times as stack shots were fired.
This should open up slots for various new character types and fighting styles.