The thing with psionics having a different mechanism than wizards/clerics/etc is that almost by definition it will either be better or it will be worse.
(the likelihood of it being comparably powerful as in "same same but different" is of course theoretically possible, but really slim to none)
I can't really agree with this! There are several levers to pull when designing a "special powers" subsystem, and all you need to do is make sure that the different subsystems appeal to different styles of play.
So far, in the core rules, we don't have much variation on the spell slot theme:
Divine: all spells known, prepare spells, spell list has defensive slant
Wizard: all spells potentially known, prepare spells, spell list has offensive slant
Sorcerer: few spells known, spell list has offensive slant, can boost spells and spell slots are fungible
Bard: moderate spells known, spell list has defensive slant
But all of these share the same slot progression, the same hard cap on spells > 6th level, and the same dependence on V/S/M components. All three can be dialed up or down for a different game play experience.
For example, someone might think the most important feature of a psionics system is that even a low-level psionic can go nova with their highest-level powers. Then we might blow the cap on 6th level and higher powers, and introduce higher-level powers more quickly. What is the fair cost of this increase in power? We can dial down the number of spell slots (or equivalent resource) drastically. Then there is the lack of components--another clear advantage that has to be balanced. So one possible framework for psionics on the spell slot model becomes:
Few powers known, powers list has defensive slant, no cap on use of high-level powers, slow slot progression compared to arcane/divine classes, no V/S/M components, powers can be boosted, slots are fungible.
So on the face of it it's similar to the sorcerer (with psi points, metapsionics, fungible slots) but it also has some unique features that drastically change the experience of the class (very different spell list, can burn points/slots to fuel multiple high-level powers if needed, no components for any spell).
Returning to your point, is this a power system that is so much better than the standard classes that players will flock to it? I don't think so. And many other combinations are possible.