After playing mostly Psyker and trying different builds I would say that he can be very powerful but has a limited variety of builds. Brain Burst is just too weak on heresy+ difficulties because it does not scale well in terms of damage or CC. Trying to manage your warp charges with it is also a waste of time because some talents can do it for you. My build is focused on damage, mobility and passive maintaining of charges. The most important for me were ranged weapons and only two are good for me.
Voidstrike staff is a fusion of Bolt staff and Fireball staff from Vermintide. Horde clear and sniping feels great, you can charge it for more damage and bigger AOE, it also can pierce enemies. Peril managment is not a problem and only downside is low armor damage but for that you can use BB.
Surge staff is just my new favorite staff in tide games. Damage is not great, horde clear is weak and peril management is a nightmare, I was blowing at first constantly from too much peril.
So what is so good about it? Crowd control is just INSANE, nothing (other than boss or crusher) close to you up to mid range will be able to move, you can zap enemies behind covers if you know how to utilitise nearby enemies and good single target/armor damage makes it probably best staff in the game so far. Your sharpshooters will fire at sitting ducks.
Brain Burst is just utility and I use it for very tanky enemies like Crusher/Bulwark or to snipe Sniper/Bomber otherwise it is just waste of time and peril.
Force sword is just too risky, you have to constantly push enemies all the time and more CC is just not worth it. Special is good but lack of cleave means you will probably waste it on some trash enemy. Melee build is just too risky for class with no movement skill and low health pool. Maybe there is some kind build that makes it possible.
Melee options do not matter much. You can go with a high mobility tactical ax or sword for cleave.
I am a veteran of Vermintide I&II but if you know of any good ,tested build on heresy+ difficulty I would like to hear it. I did not try damnation yet but completed a few heresy and even endless horde heresy. My weapons are not maxed or even close to it.