That's a really a poor option, and rather lame to be honest. A Cintiq 13" is infinitely better for the workflow you're describing and costs less( Unless you go by the paid-for-shill-youtuber opinions that were pro iPad Pro weeks before it was released ).
And I personally prefer Painter, but to say Photoshop kind of sucks as drawing tool comes off as naive, especially given the improvements Adobe has made to its paint and drawing tools in recent years. If I want to just doodle and I'm unfamiliar with Photoshop, OK, but other than that, I can not agree. There's NOTHING on iOS that remotely touches Photoshop, let alone any desktop level graphic programs. An app is an app, so incredibly limited.
And the iPad Pro is not at all worth its cost! It's not a real computer, but cost more than one, and it's not even remotely a professional product.. If it ran OS X, or if it were half the price and included its pencil, I'd have absolute praise for it.
And the Apple Pencil while good, is by no means excellent( going by your parent comment ), not when compared to what Wacom has been making for a long time now. Its tilt-support is pathetic( it's just ON or OFF ), no barrel-rotation, no side-buttons, no eraser, no support for multi-ID support( I use 3 styluses on my Wacom Companion, which is why I prefer Painter***), it's inferior technically all around, and it needs a "battery"! Some people like its pencil form factor, I don't, it's a throw back to the Artz stylus.
***I currently use a Wacom Companion( i7 model ) and love it for all of my 2D work. It replaced my MacBook Pro 17". It's the only tablet I bring with me now when I need to go remote. It's a real computer; which of course has some trade offs, but its benefits absolutely outweigh an option like a computer + iPad. I used to lug a Cintiq 12wx around with my MacBook Pro( my backpack felt like it weighed 50 pounds. ).
And here's a newer solution for what you're getting at.
:) It's the Wacom 16 Mobile Studio Pro( i7 model with a Quadro GPU ):
http://www.wacom.com/en-us/pro...
It's my next portable and the first portable in a long time, not since the first Wacom Companion and Titanium Power Books, that has me drooling. It has the power of my last desktop-workstation, so I'll be able to use it for 3D modeling and moderate 3D painting work when not near my current desktop.