I'll definitely take your word on it due to lack of time with Psionics.
Though if it is the case that psionics is more balanced, it would have been nice had they applied these same "balanced" rules to the concepting for the traditional system instead of wasting time renaming some spells, adding some new ones and creating an entirely different type of "well, its not really magic but sort alike magic" system. But ah well, I suppose there's always 4th edition Psionics, heh.
Ah, but I could argue - by that sentiment - that there is nothing actually different between divine magic and arcane magic. They're the same thing, right?
Except they're not. Even if they can cast the same spells - the character concept is drastically different, the lore around the character and material is drastically different, yet they interact with each other mechanically the same way.
As someone who loved the CONCEPT of AD&D Psionics, who was very disappointed in 3.0 Psionics, and who loved 95% of the Expanded Psionics Handbook in 3.5, I can tell you that it's ALL about the flavor and how you implement it. And that, unfortunately, isn't always an easy thing to put on paper and explain to new people.
3.5 psionics had its mechanical issues - but it's more balanced than the core magic system. How can I say that? Because core magic could do Pun-Pun better than Pun-Pun, which was originally proof of how "psionics was broken." Magic has its own issues and, typically, its own houserules in just about every game I've ever been in. Heck, there are other parts of Core (PHB / DMG) that typically have houserules because the DM or players feel it is "broken" or "doesn't work", so folks who trot out the mechanical issues of psionics as the sole reason not to implement are kind of casting stones froma glass house.
3.5 psionic rules' biggest issue is the ability to go Nova - I won't argue that. However, magic users can also go nova - it's simply that psionics more clearly shows the problem and is easier to nova with for novices.
All the classes are designed around the 4 encounter / day rule - expecting psionics to automatically be balanced in a game that doesn't follow that expectation is of course going to cause issues - just as the wizard / cleric / druid can use all of their daily abilities right off the bat and then not have to worry until everything has reset, thereby trivializing the encounter. The DMG specifically has suggestions of how to handle a party when you're not doing 4 encounters per day for a reason, after all.
As for the point about "why didn't they apply the balance to magic" - because the XPH came out significantly after the PHB, and Vancian spellcasting and the problems associated with it are a bit of a sacred cow. UA introduced a spell point system that does to magic what power points do to psionics. I've heard pros and cons about it, although I've never actually used it.
For me, however:
The XPH is about on par with the PHB in terms of balance. Take that as you will, considering CoDzilla.
The flavor of psionics as a concept is far cooler than hocus-pocus creating TVs and flinging poo, or invoking a higher power in hopes they'll grant you abilities for being so pious.
I'd rather rely on pure force of will to force the universe to do what YOU want.