"How do you compete with iOS without supporting iOS apps, iCloud, and iMessage blue bubbles?"
You build good alternatives for each of those.
You build good alternatives for each of those.
Ask Microsoft, who tried developing Windows Mobile after the market was taken over by iOS and Android. Or who still tries competing with Chrome without much success, despite it being pushed on Windows as the default, with annoying settings and ads included. Nevermind that they gave up developing their own engine because they couldn't keep up.
Nokia and BlackBerry found that out as well.