If we agree with Apple's definition of the iPad as a computer then we can probably also agree that the iPad is the best-selling computer of all time. Even off the back of a six quarter slump, individually the iPad probably outsells every other computer in production today.
That slump remains a worry. There's no question there are fewer iPad buyers out there than there used to be. The question remains why?
My guess, based on personal experience, is that the iPad is a computer with limited use cases. For most users it is a secondary device, which sits between a laptop and a smartphone without having the advantages of either.
My view remains that iOS offers Apple a more profitable future than Mac OS and that it should be moving development resources from latter in order to make the former a more capable platform.
Capable of really replacing a laptop that is.
Apple charges about the same for an iPad Pro 12" as it does for a MacBook, when fully specced out. I'm pretty sure the iPad attracts a significantly higher profit margin for Apple than the MacBook at this point.
However given the choice between an iPad or MacBook as your only device, there's no question that all but a small minority would go with the MacBook. Or, as seems increasingly, a Windows 2-in-1 device that offers the best of both worlds. The Huawei Matebook, for example, is around 25% cheaper than either iPad or MacBook, offers the best of both and includes all necessary accessories. Given the way that Microsoft is updating Windows 10 it's also likely to be usable on the latest version of its platform for as long as either Apple product.
For the iPad Apple has control of both the software and the hardware to a much greater degree than with the MacBook, which uses bought in Intel processors and also has to support any device which plugs into the USB-C port. Thanks to its Mfi initiative Apple doesn't have to concern itself with any of this legacy support in iOS. As a result the software can be more streamlined and perform better on less expensive hardware.
Making the step from companion device to fully fledged computer is going to take some effort to pull off, and more importantly the desire to make it happen. In doing this Apple may cede more of the PC market to Windows vendors, but the payback will be a position of strength as the market changes over the coming years.