If you go by people, Android has more market share. If you go by profit, iOS has more market share. https://www.macrumors.com/2017/03/07/apple-global-smartphone...
> None of that lock-in exists in China
This is true. If all your friends and family use iMessage and PhotoStream, then once you start using that too it creates lock-in specifically tied to software that only runs on Apple devices.
As an example, all my family use iPhones. We use PhotoStream to share pictures of family events and children and the like. If I were to switch to Android then I would lose all of that interaction, and so it's a big driver in keeping me (and other family members) on iOS.
Contrast this with China, where even on Apple devices, people generally use WeChat for doing that, rather than the Apple equivalent. WeChat also runs on Android and so you can happily switch platforms and you'll still have access to your same WeChat account with everything there.