Pretty much what it says on the tin. The way Warp Charge is presented as a fairly central mechanic for the class, it’s listed as an “iconic” ability for a reason. The expectation and intent seems to be very much for the psyker to try and juggle their warp charges and keep them up whenever possible, doubly so considering they’re central to several unlockable talents.
And yet, it doesn’t really seem to come together in actual play like it does for other classes. Even on higher difficulties, I find myself just plain not bothering with the mechanic at all, while it’s both simple and rewarding to play around the iconic abilities of the other classes. I’d say the reason for that is twofold: Too much effort required, and too little effect to make it worth it.
The first reason is probably the bigger one. To keep your warp charges going, you need to land a brain burst every 25 seconds. Simple in theory, but in practice that’s a significant headache. Brain burst takes a significant amount of time to charge up, to the point where it’s only really worth it to do against elites. But if no elites are around, you’re basically interrupting what you’re doing to waste several seconds just to pop a random soldier’s head. That’s time that you could be spending much more effectively using your regular weapons. And that’s not even considering practical difficulties, like your allies killing your intended target before the brain burst goes through, your peril being filled from using force weapons, or just plain running into mission sections with few/no enemies.
In practice, keeping your warp charges up is not something you can organically include in your usual playstyle. Instead, it’s something you need to be constantly looking out for, at a significant attention and opportunity cost. There are some talents that let you generate warp charges from regular attacks, but the trouble with those is that they’re random in nature and as such unreliable, meaning you’re still playing with a constant eye on your warp charge timer. That’s in stark contrast to the other classes’ iconic abilities, which usually just work passively as long as you simply play the class as normal.
Secondly, the pay-off is just… not great. With full stacks, you get a whopping 12% extra damage. That’s just not a lot in a game where most enemies can be killed in a matter of 2-3 hits, since 12% damage will often not change the actual hits to kill required. It’s only really relevant against elites, and against those you’ll be using brain burst anyway, which is still a one- or two-hit-kill irrespective of the damage bonus. There are some additional synergies deeper in the skill tree, but those tend to work off of having max charges, which again is a significant barrier.
So, what could/should be done about this? For one, make it less of an attention tax to keep your warp charges up. The simplest way to do this would be drastically extending the decay time of the charge, like outright doubling it to 50 seconds. Alternatively (or additionally), it could be done by offering additional reliable ways of generating warp charges that are more organic to regular gameplay, like through certain force weapon attacks such as the force sword’s charge strike.
Apart from that, changing the warp charge bonus to something more interesting could be worth considering. Rather than a plain and often inconsequential damage boost, something more integral the the classes other mechanics like a boost to peril reduction or brain burst charge speed would be more interesting.