Yes, spellcasting > everything else. However my reasoning is that the paragon abilities help out a martial user a lot more than an actual caster/psionic.
Potential for starters boost d20 rolls and damage rolls. A caster/psionic only really has use for it for boosting saves, while a martial user gets out a lot more mileage for attack rolls and skill checks, which a lot of manevers demand.
Then, a caster usually would've already had his ability DCs tied to one single ability score, but the martial user had to deal with each martial school having a diferent tied ability. Thus relatively speaking, Paragon warrior (replace multiple scores for one) does more than Paragon Magic (you're probably still basing yourself in your old main score).
At 3rd level when you get your second excellence, the caster is one casting level behind. The martial user however isn't actually a level behind, since paragon levels grant full IL, and you unlock new maneuver levels based on IL, not martial class level. Like Anomander pointed out, that can unlock some cool multiclassing tricks. Plus the martial user unlocked a new school and got an extra maneuver from it, while the caster is still limited to his old list.
Extra stuff like Know The Trick actually help more the Martial Paragon, since the caster could've already got those tricks any other way if he wanted to. Also as they say, if you're the caster and you're taking hits you're doing it wrong (because it disrupts your casting), while martial users are usually frontliners, so fast healing, d12 HD,resistances and DR again help them more than the caster.
Also finally, if the caster is taking paragon levels, it means they aren't taking borked fullcasting prc X levels.
I thought it was pretty obvious that, no matter how you look at it, that PRC is meant to be superior to almost every other options out there. That's why it's called Paragon. Just looking at the HD/BAB/Save/Skill progression should be a good enough hint of that.
Well, I'm seeing if I can at least keep it in the same level as the other prcs around here. Multiclassing paragon shouldn't be an auto-choice. Notice that you can'se use flaws with it (and feats are damn precious), and pretty much every ability has prerequisites of sort. The original draft had even heavier ones (like Paragon Magic demanding Combat Casting), so if people think it's too good right now, I'll be happy to put more prerequisites back. However I get the feel it turned out quite popular due to the amount of feedback.
Though, Catty is right in that Paragon can be used to exceed a caster's progression.
If a wizard goes Wizard 5/Paragon 1, chooses the Excellence "Paragon Magic" and then takes "Extra Excellence" for his 6th level feat to get "Paragon Caster", you end up level 7 on your wizard caster progression at level 6. Going into a full caster PRC afterwards keeps ahead all the way.
Read the small prints damnit! You can't take Extra Excellence until you've unlocked Greater Excellence, that demands 5 paragon levels!
Ah, gloom'd by Retrokinesis.