By 14th level, major armour is usually useless. Scorching Ray is useful on the odd chance your target isn't fire resistant, but you're scraping the bottom of the barrel to use it and you still have to hit with a ranged touch attack. Advantage still psion, because using high level psionic powers is extremely cost effective. 9 points spent on a fifth level power has a far better effect than spending 5 for third and because of that, he's uses less of his resources per fight than a wizard because he gets more bang for the buck.
As for sorcerers, they don't have a wizards versatility. The only thing they do well is fire off lots of combat spells until they're dry. Blasting is their only strength, which the more versatile psion does better. Not balanced.
Psions do have some rather nasty diadvantages:
Undead, immune to a rather large amount of Psion powers,
Only telepathy and some psychometabolic really. Kinetics and psychoportation still work fine. They're also immune to all sorts of mind effecting spells and compared to how hard outsider energy immunities hurt arcane casters, this isn't that bad at all.
Anything requiring a major Fort save, especially poisons and diseases, doubly so if they cause a lot of ability damage or permanent abilty loss
Same with arcane casters.
Demons, Devils, ect. Such creatures have Psionic Resistance equal to their Spell Resistance.
Arcane same.
6 words, The Essential Guide To Mind Flayers, as completely nasty as they are normaly useing the guide sends Psi-players into the realm of Lovcraftian horrors
Uber mindflayers hose everybody.
Social stigma: An optional way of taking them down a notch, from the second edition book actually. Having one or several religeons having psychics on the 'burn at stake' list, and looked down on in places that don't kill them on sight. As persona non-grata virtually everywhere they are extremely rare, so NPC psions to train them are hard to find.
This option turns their 'hard to spot' advantage into a liability when it comes to social situations when they are discovered.
Campaign world specific. Darksun has the reverse, to add insult to injury and psionics are much easier to conceal or disguise as magic with a few gestures and nonsense words.
Hitpoints: The same
So the only advantage arcane has is that they can trade having fewer powerful high level spells for having more weaker lower level ones. All the psionicists disadvantages apply equally to arcane casters, who don't have the psionicists advantages.
The Excellent Prismatic Spray. For when you absolutely, positively must kill a motherfucker. Accept no substitutions. Contact a magician of the later Aeons for details. Some conditions may apply.