At 20th, when the MT finally (FINALLY!!!) reaches 9th level spells, the difference is not so pronounced. But at all levels prior to that, the MT is behind at least one, occasionally two spell levels. Play a 7th level straight Wizard, then a 7th level MT build, and the horrible underpoweredness of the latter will be readily apparent. 20th level builds have very little bearing on actual in-game performance - especially since many, if not most games never reach the highest levels.
The MT did indeed look broken at first - until people actually sat down and tried it out in play. That's why I'm saying "give Mystics a chance!" - gametest them.
I appreciate your balanced perspective.
As you pointed out the MT, despite what one would think would be amazing synergy, was still considered under performing when compared to a straight caster of either class.
My class begs the question... is anything the mystic can do in a single round significantly more powerful than anything a standard wizard can do in a single round?
If you find the Focused Specialist to be balanced then the answer must be no.
The FS sacrifices a single feat, and three spell schools and gains two bonus spells per level as a trade off. At 9th level this is huge, if only for the metamagic spells you can also put there. Why everyone and their brother isn't a focused spellcaster is a bit beyond me. As a conjuror having a couple extra copies of gate handy will solve almost any problem you can think of, or shapechange, or timestop, or whatever...
So, as a chassis the Mystic is the Focused Spellcaster pared down. Instead of bonus slots and feats he gets access to Psionic Powers..
And that's kind of a hard thing to weigh. So you still have to come back to the question... is anything a mystic does in a single round more potent than what a wizard can do... and the answer is still "No". The argument could be made that the Mystic has greater options than the Focused Mystic... but this would be misleading. The Focused Specialist will use his bonus spell slots for the school of magic he has built his character around, be it evocation, or divinination, or enchantment... whichever. The rest of his slots will be for breadth of option. A psionicist may only ever learn 36 powers I believe, so the Focused Specialist still retains a greater breadth of options. He may not have the same depth (i.e. all of the psionicists power points may be burned for 9th lvl powers... Your average 9th lvl power, used as a 9th lvl power costs 17 power points I believe. If a Psion used every single power point he had to manifest that 17 point ability... he'd get roughly 20 manifestations or... roughly two spells per spell level...
Keep in mind, however that the mystic gets neither bonus spells from intellect, nor bonus power points from charisma.
This of course brings us to the various bonus abilities of the Mystic. Chastise is not a game breaker... and in fact is more thematic than anything else. It is completely unenhancable to my knowledge and works against a relatively small, though pesky, subset of creatures.
Watchful Spirit would almost fall under the same category but it has the potent ability of being able to reroll initiative... which can be extremely useful to a caster... but even watchful spirit cannot compete with the bonus feats a standard wizard receives.
This then is why the Mystic gains access to a single vestige at caster level -5. Naberius, Haures, Balam, Zceryll, and Arete seem to be the only ones that are significant... maybe Shax.
), then advancing slower than either the party Wiz or Psi is a good start. A Gestalt Sorc | Wilder minus the Wild Surge would be cool, but roughly on par with an Optimized Wizard or CoDzilla. 
