> Surely if a lack of open phone OS and feature access was the problem, we’d see a rich ecosystem of integrations that exist on Android devices that are just impossible to achieve on iOS right?

It's entirely possible on Android? Pebble used to have decent integration with Android, from notifications/calls, to music controls, to sports tracking/health data. You could even get navigation integration! And that was a decade ago. That's what makes it so painful: the pebble android experience is really nice and integrates very well, while the iOS one is terrible due to the Apple lockdowns.