It doesn't have to be, though. Just like iMessage is hugely successful despite being limited to Apple devices, and even then widely differing in features and re

It doesn't have to be, though. Just like iMessage is hugely successful despite being limited to Apple devices, and even then widely differing in features and reliability, for example, between iOS and macOS. A wonderful collaborative experience could just be a USP for the platform. FWIW, the now obsoleted iChat was way ahead of the curve compared to the current iteration of FaceTime in group settings, anyway.