Deathslinger is objectively the worst killer
Okay so I've just finished playing deathslinger for about 12 hours straight now and I think I can confirm he's worse than any killer we currently have. I'll prove it by comparing him to clown who most people agree was the worst. Each time deathslinger fires he has the clown's slow from throwing a bottle and each time he reloads he has the clowns slow from reloading but what do each of their powers give you? a deathslingers shot should give you a hit and deep wound or a hit and down. But you can counterplay his power just by dropping pallets, sitting at certain loops, having a friend sprint up and take the hit for you (which doesn't apply the deepwound to either of them) and if he misses he gets slowed by the shot AND by the reload. Clown's power can deny loops and slow survivors as well as mess with their vision and with addons even apply exhaustion or slow them further and you can't really counter play a good bottle besides baiting him to throw it where you aren't going. So in theory clown can almost always capitalize on a bottle by making chases shorter and he can throw several without needing to reload.
But lets ignore all of that and look at only the numbers. Both abilities slow the same amount for the same duration if not deathslingers slows him for longer. It takes clown 5 seconds to reload all of his bottles which is 4. It takes the deathslinger 2.75 seconds to reload 1 shot the clown has already saved more time than the deathslinger if the deathslinger has to reload twice. Then add in the clown is 115% and the deathslinger is 110% meaning even if you completely removed their powers the clown can end chases faster.
The only real advantage deathslinger has over clown is a smaller terror radius and his ability to theoretically get an injury or down from 18 meters which has a lot of ifs such as cover and other survivors.