Both have their perks
In the Jester's high-level game we have both examples. When 3.0 started, Sybele started as an archer based fighter, and then added a lot of psion levels when the original psionics handbook came out. Its worked pretty well for me so far.
With the XPH, I've had to redo alot of my powers to focus on buffing myself though, b/c at the level we are at I will rarely be able to penetrate enemy SR for reasons presented above. I never have a high enough save now for psionics now that its based all on Int.
As a psion you have a large breadth of powers available that a psychic warrior doesnt. At least as an egoist, Im a competent back up healer to the primary cleric. Lets hear it for shapeshifting your way back to health!
Angel, the Psychic Warrior, finds herself mostly as the tank. Whereas, I am more of a tricky archer support person, but hey - everyone's made it well so far.