To understand where the iPad Pro fits into the world, you have to understand that the shift from laptops to tablets is more of a generational shift. The same thing happened with other technologies such as the car. The car was noisy and a menace to children. The horse was graceful and gentle. Because their whole workflow was already setup around the horse and places that the horse could optimally go, they couldn't see the advantages of the car. You basically had to have a whole new generation take over from the previous one before the horse finally went away.
You have your apps, your workflow, and your habits set and refined over many years and they work perfectly for you, so why change? There's no incentive. But when you watch a lot of young people, people who grow up on mobile devices, you realize that they don't come with any of this legacy baggage. Touch is Star-Trek intuitive and mouse manipulation is archaic. Many of them are perfectly happy to bang away at a short essay on a glass keyboard because they've been doing it since birth. So that's who the iPad Pro is for. This is what Tim Cook meant when he said that the iPad Pro was "the future of computing."
The product is not quite there yet and will take another product generation or three to refine, and the key user groups for the product are still quite young, but Apple has no choice. It has hypotheses about use cases that need to be tested and refined in the real world and it can only do that by shipping out real products.