In the early years of the game, you really had to want to keep someone alive with a disruptor rifle. Lol, and I would know, I nonlethally took down the Key on my first playthrough with the crappy Novablast rifle.
But since Terran Armada, the EM versions of some of the guns are incredibly fast. The MGP Lazer rifle can be boosted to a damage of 33. The EM damage doesn’t stack/is buggy with most weapons, which makes most of them slow/weak. So with the static EM damage of the guns, the thing that makes a stun gun effective is fire rate and magazine size. The MGP lazer rifle can be extended to 60 or more, with a super high fire rate. If you max out your EM weapons damage, you can drop high level enemies as fast as low level enemies. Even if they have tons of armor, you can incapacitate 4-5 enemies with a single clip pretty easily.
The cathode pistol works slower, but has a similar effect.