It did indeed exist, and also there is still a rifle that stuns, the Agrotech DMR-AV the stamina surpasses the health damage(at least listed in-game it is, but on APB:DB they equal out.) I get a fair amount of stuns with it accidentally from afar because health damage diminishes at range drastically while the stun doesn't as much It feels like.
I feel like a screen blackout would be nice to visually stop it but voip is still a factor and that you can be rescued by teammates so you wouldn't know when to get back in the action.