More than one way... movement is key though. I'm certainly not buying that downhill plane is totally BS. But, there are still more variables involved.
Kyle and gang are certainly more qualified than I am and I'm not backing this up with any science or analytics but, IMO... There are tall P's with a downhill approach but their spin and release result in a slight tail that negates some of the downhill efforts, making them quite hittable. There are shorter P's who have a natural over-the-top motion and their release and spin result in added downward movement. These guys can be very tough to hit. Any type of significant movement from the initial perceived track will tend to make for an effective FB. I do know that, as a hitter, it was always tough to step in the box and feel confident about putting a good swing on a hard pitch that had good downward plane and movement - just didn't stay in the path of the bat long.