Zappa had a preternatural vision to what would become his Music. The fixation on Ionisation, and the famous phone call to a "Mr Varèse in Greenwich Village", for instance, reveal a difference between Zappa and other geniuses that truly amazes.
"Normally," geniuses are influenced by what they find on their road. Zappa himself mentioned he could have developed himself into a genius entrepreneur. Or he would have excelled in politics and become a party leader and a president. But no, Zappa wanted differently. He purposely created a continuity of events leading to his "becoming" -- his emergence as Zappa. So my take is that Zappa is one of the few "meta-geniuses" of this world. Varése was a fundamental encounter/ingredient, but for reasons that escape my meager ability to understand, it seems like Zappa-in-progress knew that he needed Varèse, he needed Strawinsky, he needed Webern, he needed Cage. Don't ask me how, but he seemed to select those elements, those encounters. As if they would help speed up the process of his emergence.
Because speed and time were of the utmost importance for Zappa to become Zappa.