Ok, right now it looks like they are not really strong and might die easily if 2 or 3 peopel attack one at the same time, considering the fact that most of the psionic abilities are channeling. They look like an "off-station" threat, like wizards or nukies, however dont hold the surprise factor, and are not disguised as a normal crew like vamps or clings.
First of all, i think we need to decide if they start like a crewmember (like cling, blob or sling) or start off station, like wizard.
Also if they fight eachother, i think they should be much stronger in crew vs psi fight.
For example, imagine this: every light source (lighter, torch, computer, mushroom) is not working in a certain amount of tiles around psionic. They are invisible like revenants - invisible unless use abilities. (not invisible for other psionics). In their presence crew are automatically affected by terrifying hallucinations, which deal real damage, therefore normal crewmembers, before they evolve a method to fight a psionic, should run and hide, or monsters and terrors of psionic will consume them. Not sure about the weapon against the psionic tho. Imagine two wizards fighting onboard cyberiad, constantly teleporting and throwing fireballs, but also invisible, so the crew are just little puppies caught in a crossfire. Thats how i see it. If they are not scary at all and have to hide in maint themselves like slings for example, and along with it have to fight other psionics, they might look like a bunch of nerdy kids not worthy any attention of crew.
This is my happy little thought