@astearns, in situations like that the gestures can be integrated in the app. But an explicit “back” button is different. it is a browser control. Why replicate it (often with different behavior)? We learned this lesson on the Web a long time ago. Site’s that tried to rebuild the browser’s back button moved away from it real fast.
If you need navigation actions make them navigation actions: ideally labeled with their destination/function and secondarily with a non-“back” label like “up” a nav tree or “previous/next in a sequence.