This does sound like it could be a good compromise by allowing the enumerator to make the zoom level decision once.
Agreed. Given that no users have jumped up here to express enthusiasm, I don't think we should change the default.
This also seems like a reasonable approach to me. Presumably the form designer would field test the change so I don't share @yanokwa's concern about being annoying to enumerators. That said, having Collect remember the zoom level has the advantage of letting each enumerator have what they need based on their eyesight, device size, device pixel density, etc.