Producing a list of all the things that aren’t in the iOS version would be very time-consuming, and not worth the effort—it would probably take weeks of combing through the user manuals. I would say it is easier to describe what it is. It is not in any way meant to be a replacement, but a mostly content-focussed tool for on the go. It does have some higher level management, like a sidebar, and on the iPad a very simple take on the corkboard idea, but for me anyway, it’s more about giving you a way to drill down to content easily, as opposed to how the Mac/PC honestly has more features for item management than text editing.
Or to put it in a way that measures how much there is to say about the software: the Scrivener for Windows user manual is 760 pages long, the Mac manual is 910 pages long, while meanwhile Scrivener for iOS doesn’t have a user manual, nor does it need one. It has a short tutorial, and we get hardly any questions about how to use the program itself.
Speaking of the tutorial, it is available from our website in both PDF and .scriv format, and serves as a pretty comprehensive overview of what it is, rather than than what it is not. If you don’t see something mentioned in there, it doesn’t have it (with a few very minor exceptions I think).
See also:
-
Making the mobile version as capable as the desktop version
As I note at the bottom of that thread, if you want a more seamless experience while mobile, a Windows tablet will be a much better option for you (just make sure it isn’t ARM). Whether or not that’s a good choice for art, I don’t really know—probably with the more traditional route of drawing with a separate tablet and stylus, rather than directly onto the screen.
-
PC vs. iOS scriv: how's the usability on iOS?
This thread has more focus on overall capability between systems, as well as Scrivener. With iPad you are giving up a lot. That’s part of the appeal as I understand it, for some, but this notion of how cut down Scrivener is is something you will see across the board in everything, all the way down to how files are managed, or how text is selected.
If you can do so, it would be worth hanging out in an Apple store for a while to see what it’s really like to write with it and so on. I entirely agree with what someone had to say in that second thread, where the whole system just feels too clunky. Even though the thread is old, I don’t feel much has changed in that regard. Merely positioning the cursor back before the comma I just typed feels like an edge case to Apple, something nobody does so why bother making it easier.
But obviously a lot of people feel otherwise, or they wouldn’t make the huge sacrifice of selecting a device without a keyboard as a writing tool! It must be doing something right, for some. 
Art… like you say, that makes all kinds of sense.
Syncing: up to you whether it’s worth that or not. There are plenty of ways to get work on and off without it.