Swipe to go back support is pretty wide if you select for iOS-first apps (I do). It’s glaring when I try to use it and it’s not there, so when that happens I’ll either go find an alternative or drop back to the web app (where Safari will definitely implement it).

My Android devices all have the gesture bar enabled because the old style button bar is an eyesore and easy to trigger accidentally (Android’s swiping from the right to go back is also too easy to trigger as a right-handed person, but that’s another story).

My metal model for the undo/back split actually follows desktop browsers. Cmd-Z isn’t going to undo navigation while Cmd-[ will, and so the two are separate and distinct.