ehm... mystic is something else
what guru did on namek was called hidden powers if I remember correctly :S
Mystik is what gohan gets at the end of buu saga, it's a powerup that gives u the abbility to use ur full power, wich is , in gohan's case, extremely powerfull. At mystik (without ssj turned on) he's the 2nd stongest fighter, if he would turn ssj on, he'll be that strong that the earth would explode just because he transformed, imagine what ssj2 will do
EDIT!
*Im referring to the game, That IS what this threads about isnt it? and your theory about Gohan is merely supposition, NOT fact*
Cheeseman