Have you considered that even if your premise is true, the keyboard can still behave differently between apple apps and non apple apps. Let's say non apple gets the standard unmodifiable keyboard that you speak of and apple do some invisible to the dev/phone user enhancements to the input behind the scenes in their apps thinking they're making it better and it's these enhancements that fuck up the experience while everyone else gets plain old unvarnished text. As a swipe to type user non apple apps subjectively give a better experience.