When Steve Jobs first announced the iPad in 2010, his presentation contained a telling slide. An iPhone and a MacBook parted to make room for a middle device. It would be best at a few important things, he predicted: web browsing, email, photos, video, music, games and e-books.

Despite the iPad’s early success, people started doing more of those things on their phones—especially as their screens got bigger. So with the iPad Pro, Apple changed tactics. The Pro, particularly the newest model I’ve been testing, can likely do...