The force staff weapon group have a bit of an issue that 3/4 of them share the same primary attack, meaning that there’s only really their secondary fire mode to distinguish them. And as it stands, the voidstrike staff stands head and shoulders above the others to the point of making them redundant. Particularly at higher difficulties you’re just making things harder on yourself if you take anything else.
Note, this is very much not a call to nerf the voidstrike. As it stands, it’s currently kind of the one thing that makes a psyker worth bringing compared to a veteran at higher difficulties. Instead, the other staff types should be improved to match. Let’s take a look at them in turn
Voidstrike Staff (shoots an exploding projectile): The gold standard of the class. It offers exceptional crowd control and area damage at range on short notice, and even substantial stagger and damage against elites. Any other staff will have to be able to offer something at least similarly useful to be worth considering.
Surge Staff (shoots lightning): This one is arguably a close second already, as it offers decent crowd control on short notice as well. Its main shortcoming is that it only affects a limited number of targets and also does not cause all that much damage. This one might be helped by an increase in damage of its secondary, especially against armoured targets, to tune it more towards a group killer particularly against dispersed squads of shooters in cover, rather than a primarily CC machine.
Trauma Staff (creates ground-based explosion): This one is trickier, as it’s kinda just Voidstrike But Worse. Its secondary has about the same effect as voidstrike, but at a shorter range with longer charge-up and trickier targeting. Rather than messing about with its secondary, the solution here might be doing something with the primary attack to set it apart. Something like giving the regular bolts limited penetration might be worth considering.
Purgatus Staff (psyker flamethrower): This one is just kind of bad altogether. Yes, it’s very good at killing hordes, but in return its quite bad at everything else. The lack of any long-ranged capability is just too much of a downside to justify a situational benefit. This one could really use a primary fire that has some actual range, though ideally not just yet another copy of the basic psybolt. Perhaps an arcing projectile that causes a burst of fire where it impacts, something along those lines?