Essentially, we are back to "The system is bad so it is time for some houserules!" solution that isn't the very bestest thing to have. So to say.
Properly designing a challenge for your PCs isn't "houserules" it's the GMs job.
Also, I note that a group of characters without a psyker could have achieved the same outcome in your encounter by tossing in a hallucinogen grenade... so again, it seems to me the problem, if there is one, isn't with the psyker rules.