I can prove this does the most damage with math.
 Hive Scum Build - Warhammer 40k: Darktide 

For those who yearn for murder.

Zero defensive utility, full aggression. Don't take to havoc, sweep anything else. Don't forget to dodge or you will eat shit. Don't make any mistakes.

Right, said I would explain. There's the most damaging melee hive scum build if you ever play one. I can defend every talent choice. Have a mod that tracks uptime on blessings and perks. Was making it so another friend could see as well. I was playing the game anyway, figured I might as well prove to myself which hive scum knife melee build objectively did the most damage with minimum defensive investment to survive.

The reason I have blackout grenades is it directly counters the one thing that can stonewall you: packs of 4-8 crushers. You have mediocre damage on these.

Pistol 3 taps crushers so you can soften them if needed.

The grenades knock crushers flat on their ass then you can pick them apart. You generate infinite of these bombs every close range kill, and you will be getting plenty of those. This combined with the pistol means if you had to you could slowly but surely pick apart 20 crushers if you had no choice.

They have absurd finesse damage which multiplies crit damage to obscene levels. Knives have almost 100% crit. You always get most value from precognition/reposte.

The knives will kill anything but heavy plate armor with one swipe. They have the highest finesse/crit damage modifier in the game, and you always crit.

There's no need to invest in any other type of damage but carapace. Everything else is a waste, you will just overkill it. There's no need to put anything into flack damage ect because of this.

For the keystone that buffs melee damage? Zero reason to ever use anything but the node that increases duration from 10s to 20s. I know I've used that keystone without that, and I have used it with all the other variants. With stoked rage alone that melee buff will be active 90%+ of the time. Without it it will be up 60-75%.

Rampage doesn't need any node investment to have it up for the entire duration of any fight. It refreshes every attack baseline, and you attack very, very fast. The daggers already one shot everything but carapace. With the cleave node and battering strikes you have +100% cleave, 100% chance to crit, 200%+ extra crit damage.

I invested absolutely nothing in extra defense other than what is required to survive. If you dodge and avoid specials properly you never get hit so there's no reason to invest in defenses outside the required talents the class needs to function (precision violence, burst of energy, hive city brawler. You will eat shit and die without these every time.)

The rest of the defensive talents are padding if you are warming up and aren't playing the class to its full potential. That's on you. Dead enemies cannot damage you, so kill them. You can use the defensive flex talents, but you will always be sacrificing damage output. 

Again, I know, I tried them all one after another, and compared the numbers as I spammed missions.

I went through every flex damage talent, blessing, and perk, trying each one then looking at how much damage all the flex talents added to my total damage, and looking at their total uptime for the duration of the mission.

On average?

Adrenaline rush averaged 95% uptime with this build.

Rampage 30-40%

Riposte 40-60%.

Precognition 20-30%

Battering Strikes 75%

Float like a butterfly, quick and deadly? Which claim to proc from the same successful dodge as riposte and Precognition? Took me way to long to figure out why riposte and these didn't always add up. Well, 

3 second duration opposed to 6s from riposte, 2s from precognition. Average?

Each is up 33% of the time. Right.

Don't forget to dodge or you will eat shit. Don't make any mistakes.

Godspeed, and shine on you crazy diamond.