ProCreate (according to my girlfriend, who has a degree in illustration) is absolutely second to none with regards to completely eliminating the friction from digital painting.
The toolset & UI/UX feel like someone who had used Photoshop with a Wacom tablet for 10 years took everything they liked about interacting with Photoshop and got it right, and everything they hated about Photoshop and fixed it.
The app itself is absurdly responsive on a 2018 iPad Pro. I don't know if you saw the Hobbit in the theatres when everyone was freaking out about the frame rate because it felt too fast? It's like that, but enjoyable. Every other app on my iPad seems sluggish in comparison, and I don't even know how. (And don't get me started with comparing it to Photoshop, even on a ridiculously beefy machine with a 144Hz display.)
If you want something with the grunt to handle a big photoshop project, you generally don’t want a Surface, you want a proper workstation.
Using a Surface is the worst of both worlds, only really useful if you’re beholden to doing things in that way for some other reason, like it needs to be photoshop for interop reasons with other businesses, and it needs to be done on location.
Also, I found that iOS is just built for touch from the group up, unlike Windows, and when combined with well-designed app like Procreate, it just made every interaction with the screen with your hand and Pencil when you drawing so smooth and natural. It's just mind blown for us who draw for living. It just do one thing we want really, really well. Before iPad and Apple Pencil comes, the closest thing to draw directly on screen is the uber-expensive Wacom Cintiq, which mostly used by studio and serious professional rather than individual.
Windows and Photoshop on touch device is quite usable for drawing. I'd say, it is much better than in the past. But once in a while you'll end up running into some software quirk and lagging experience, miniscule menu to click on, some part of software that didn't design for touch, etc., not to mention that Photoshop is ultra-ultra bloated software. It never natural to work on it.
Anyway, I understand why people that's not into the art field didn't see the use of iPad much. It's still a big iPhone to many people, and yes, its file manager and multitasking is garbage.
In fact the Wacom is better by a large large enough margin that she’s willing to forgo using the (reasonably well-designed) Surface for the bastard child of a laptop that is the Wacom Cintiq Mobile Studio Pro 13.
Wacom has MobileStudio that runs Windows, but it also come with heating issues.