Justin Williams:

The iPad Pro is a device that is begging for great third-party software from both large companies like Adobe and Apple, as well as the smaller guys like Gus at Flying Meat. A larger screen, keyboard case, and a Pencil aren’t going to solve those problems. You can’t have a Pro tablet without pro apps to go with it. There are a few great iPad apps out there, but most of them feel like minimum viable products at best.

Exactly. I don't think iOS is necessarily holding it back, but lack of pro software is definitely holding the iPad back.