One thing that I find really irritating with psykers is how warp heat can sometimes spawn those big demons with the clubs. Those things are tanks, and the only way to really kill them without having a long, drawn out battle is to use a bunch of hard-hitting psyker powers which, of course, create more of the demons.
To make matters worse, I find it really hard to manage warp heat in this game. It ramps up so quickly and takes so long to get rid of. Maybe I'm not using the right pieces of equipment or perks or whatever, but it's really frustrating. Even more so when a lot of the negative effects created by warp heat pretty much one-shot kill you. I'm getting better at recognizing them as they appear and adjusting accordingly, but it sucks getting one-shot killed when max warp heat is, without significant investment, pretty much unavoidable anyway. And that perk that increases the number of positive effects really doesn't seem to help that much.