....... Cause your restricted to only Vai's sound.
dude...I have to disagree with you since I own these equipment.
I had a JEM555 with the same pickups as Vai and I also play it through Vai's signature amp the Legacy and the cabinet...with that combination I can nail jazz, blues, country rock, classic metal, pop, hard rock, heavy metal tones....WITHOUT sounding like Vai.
...in short...it doesn't mean if you buy a signature equipment you WILL sound like the person endorsing it.
....you CAN, however, sound like him....and thats ONE of the sound you can get with the equipment...so it's up to the user.