You aren't supposed to be able to get double kills with the Pistol. It helps you defend yourself from respawn until you can find a better weapon. Also, don't complain that spamming it makes whether you get a kill or not entirely dependant on luck. That's what happens when you spam, and what is supposed to happen when you spam. Pace your shots and keep zoomed in and it's entirely possible to get kills with the pistol. Also, have you considered moving as a group with your team-mates? If you work together you can quite easily kill players with DMRs using nothing but Assault Rifles and Pistols.
Also, it's not difficult to beat a DMR user with your pistol. Just get in close to them. People don't complain when they get killed trying to snipe a Shotgun user at close range, so why they get frustrated losing to the DMR at mid-range always confuses me. The only real problem is that the DMR is effective at every range, especially without melee bleedthrough, so you don't even have to worry about being tactical with weapon selection.
It encourages map movement too, which the DMR doesn't. The DMR can fire across such long distances that it's not safe to move around on open maps - you've played Hemmorhage and Spire, you know exactly what I mean. Plus it's so powerful that there's no incentive to pick up other weapons - the Needler, the Needle Rifle, the Plasma Repeater, all are better than the Assault Rifle, but worse than the DMR. So you end up with a situation where everybody only uses the DMR, which just isn't fun.
I also don't like that players have a better chance to beat power weapon users with the DMR. That' the point of power weapons: you beat them through teamwork and getting better weaponry of your own, not just by respawning and immediately having a perfect gun for the job.