"Guck Funners!" - Absurd Crit Chance = Absurd Survivability!
 Psyker Build - Warhammer 40k: Darktide 

I think no build in the game more epitomizes the idea of being an all-powerful warp-fuelled psychic wizard than this one. If this idea intrigues you read on.

Primary fire on the Surge Staff is very powerful with the absurd crit chance that being critical Peril gives you by way of Warp Nexus paired with the Surge Blessing and the Surge staff's naturally high crit chance. Disrupt Destiny & Scrier's Gaze both maximize the potential of the crits you're getting and Warp Unbound gives you 10 seconds to be at full Peril, unleashing your most damaging, high-crit-chance bolts as fast as you can quell-cancel them out. NOTE: Warp Unbound is *NOT CURRENTLY RELIABLE* at the exact moment you hit 100% Peril. It is best to train yourself to allow Scrier's Gaze/charging an attack to get you to 100%, then resuming fire.

All of this offense is both literally and figuratively your best defense, with Warp kills, Crits and Quelling all giving you back toughness, you can slide-quell around with Scrier's Gaze active to generate Toughness between engagements, then fire at head-height into the horde for nigh-unlimited Toughness generation as every shot is a kill, some of which are crits, all giving you 7.5%+ Toughness. You're also particularly well-suited to hunt anything that shoots: Disrupt Destiny frequently highlights semi-hidden ranged enemies in my experience, and you can better survive gunfire than nearly any class with a high enough fire-rate via quell-cancelling, your huge crit chance and Empathic Evasion. You generate more than 1 crit-per-second if you can quell-cancel fast enough, and nothing is more satisfying than cutting down a row of 10+ Gunners impotently shooting through you as you pew-pew crits into their domes.

What is quell-cancelling? Basically, you tap quell immediately after firing and it allows you to fire bolts much faster than just spamming left-click. Roughly three times as fast at optimal levels. "Perfect" timing is to tap primary-fire for 5 ms, wait 20 ms, hold Quell for 140ms, wait 20 ms. Any faster than this and either the shot isn't registered, resulting in a "double-cancel" without a shot in between, or the quell isn't registered and you get the standard delay instead of the quell-cancelled delay between shots every 2-3 shots. The goal isn't to keep quell-cancelling up indefinitely for every shot; reliably doing enough enough in a row to down the thing you're targeting with a little break in between to prioritize a new target seems to be the best balance between effectiveness and not getting an RSI.

I bring the force sword in the Melee slot because Deflector + Kinetic Deflection is an absurdly powerful defensive option. Also, the Special Attack coupled with Uncanny Strike is particularly strong because it allows for rapid stacking of US coupled with a powerful stagger effect. The incredibly good first Light attack of the Deimos charged up with the Special is a great opening strike on a Crusher, and a Heavy attack follow-up is normally enough to finish them off, depending upon your Peril and presuming you can hit the weak spot with both.

The above said, if you can quell-cancel fast enough, you should rarely if ever need to pull out your melee weapon. Every staff attack is a one-shot on basic grunt enemies, and you can quickly clear a path through pretty thick clumps of dudes to reach a pesky Elite or Special on the other side. You delete the most annoying enemies incredibly fast and are largely a defensive powerhouse by way of Toughness regeneration as long as you have a target-rich environment. You can make a pair of Crushers/Bulwarks entirely ineffective in a pinch with the Surge's Secondary attack, and if you toggle between pairs you can keep 4-6 more or less harmless while your team cleans them up. No Crusher should ever successfully complete an overhead while you are around. The secondary at any charge level is a guaranteed knockback against a Pox Hound/Burster/Trapper, and two are enough to stop a Mutant in its tracks. It's a potent defensive tool for a lot of the most dangerous stuff to your party, so don't be tempted by the allure of your warp-minigun and leave it on the table all the time.