Exactly this. And in addition, I think there's lots of potential for touch screen users. As soon as you do not have easy access to a physical keyboard, pie menus can provide a great alternative to keyboard shortcuts.
A giant button in the middle of all apps?
So you could select an item extremely quickly with just two swipes. And there are already quite a few items at level two! If your top-level menu has eight submenu items and each submenu again contains seven items (+one to go back to the root) you have already 56 possible items in this menu. And you could select one of them in well beyond a second, even without looking at the screen!
There used to be a thing nearly a decade ago to do this on Android, before the current gesture navigation:
https://www.androidauthority.com/permanent-navigation-contro...
the menu itself is pretty good, especially with the Apple Pencil, which you'd be using to draw on the iPad. Image editing/3d modeling software tends to need a lot of UI, and I think it makes sense for the most part. these tools are hopefully used by everyone. that means more sporadic use — if I'm only opening your app a couple times a week for a couple minutes, I probably won't remember the keybaord shortcuts. not to mention people who are unfamiliar or don't use keyboard shortcuts at all. anyways, bit of a rant since it doesn't answer your original question, but we should consider how to make our computers computable by all users.