This is one of those neverending debates. Everyone has their own opinion on what is and isn't a hypercoaster, and since there's no specific definition, the argument will go on together.
But to answer your question, yes, Magnum was the first hypercoaster. Why? The term was first coined to describe Magnum -- not Moonsault Scramble.
The end.
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Matt Lynch
Co-Webmaster, Kennywood Boulevard
http://kennywood.coasterbuzz.com