> but it's dishonest to present the lack of indication as a point against Android when iOS doesn't even have a precise analogue of this

No it isn't. This whole argument just boils down to whether it makes sense to require an unlabeled backward pointing arrow to be present at all times in all UIs. In practice it doesn't make much sense to require a button that isn't always used and doesn't always do the same thing just for the sake of returning to the previous app from an empty navigation stack when you need to do that occasionally. iOS might not do it, but this comes with the added benefits that no back buttons anywhere in the iOS UI is ambiguous.