It is possible to compute all outputs in parallel with a quantum computer, but what you'll end up is an unintelligibly entangled state. What you really want is

It is possible to compute all outputs in parallel with a quantum computer, but what you'll end up is an unintelligibly entangled state. What you really want is a single output, and there's no generic way of disentangling the entangled state in a useful way. The reason why numbers can be factored faster using quantum computers is precisely that factoring has an algebraic structure which can be used to achieve this disentangling.