Redundant in fantasy RPGs that already have other sources of magic.
In "sci fi" RPGs it may be fine, as almost all sci fi is just ancient myths repackaged into a modernist paradigm, and "psions" are just space wizards.
This is the challenge in adding psionics without it just being another flavor of magic. I'm all for burning shit like firestarter, but they need to be able to do things wizards can't and that takes more effort.
More effort? How about less?
The difference between psionics and magic should be that one becomes, or is, natural to the user, while magic is learned, based on knowledge of arcana, remembering rituals, spells, runes, and still disconnected from the user. Something he harnesses and uses, but does not necessarily own. The wizard, mage, or sorcerer can forget how to cast spells, they can be shut down by tying their hands so they can't make gestures, or muzzled to prevent them from reciting incantations.
In my mind, for a psionic, the powers are second or even first nature. As they grow more powerful, it becomes completely normal to them; if the power is telekinesis, they no longer even instinctively ponder reaching for a mug of mead with their arm, their first instinct is to pull it with telekinesis. Just like you or I probably don't consider using our arms - you don't go "I'm now going to stretch my arm out, grip the mug, and bring it to my mouth to drink", someone for whom telekinesis comes naturally doesn't think "I'm now going to use my magical ability / incantation / ritual / spell to pull this drink towards me". They just do. Their mind is outstretched, somehow not just more aware of their surroundings, but in partial control of it.
Then, the environment becomes their body, because they're not contained within their physical form. That mug is at their disposal whenever, they don't have to "wrestle" for control using their arm. It's a part of them, and their perception of their own body expands because suddenly, they can reach a lot more than what their physical form can reach.
You can train yourself in it just like a person might train themselves to run better, have better stamina, lift more or become more intelligent or perceptive, but it's still natural. You're not practically begging the mug to come to you by "casting a spell". It's yours, and you just grab it. Is there still a chance to fail? Sure, a dexterous person might snatch it out of the air, and your telekinesis might not be strong enough to wrestle it out, just like they might do the same to your arm, and then you might not be strong enough to win the tug of war.
Unlike a spell which can "fail and fizzle out", where "the fireball simply never even forms", a psion would, in my mind, always succeed at
attempting what they want to do. If the object is too heavy, the person's mind is too strong, or someone actively fights them, maybe they can't do it, just like a fighter's blow with a sword can be blocked or dodged; but they never fail to perform, the opponent always feels the psionic "power"...
Things outside your body become a part of you because they're just as easy to manipulate as your body is. You gain ownership over most things simply by the virtue of having almost total control of them. Again, you're not "borrowing" power from some magic, from a spellbook, or a scroll. You simply
do, and if you've trained your "brain muscle" well enough, then you do whatever you want.
It should take less effort. It should just be difficult to advance in, just as difficult as raising your STR/DEX/INT/CHA etc is.
