If one app activates another (camera -> album -> photo editor -> share), how do you go back from mid-way if you decided to?

Because Android features this metaphor, it's used extensively. Because iOS doesn't, it isn't as much. iOS features different metaphors which achieve the same outcomes in different ways, such as pop-up sheets for the camera, album views and share panes.

And in cases where one app does activate another, you can go back one step by tapping the top-left corner of the screen. There's only one level of "app back", but that's plenty since iOS doesn't tend to jump you between apps a lot, and because that navigation isn't co-mingled with other "back" operations.

There is a link at the top left of the screen that goes back to the previous app during these "app activates another another" phases.