...and one PM to manage all 4 teams and ensure that there is no feature-drift between the various OS-target versions. </sarc>

I am really just trying to emphasize that there are tradeoffs lurking everywhere and they are often hidden by assumptions.

Telegram already does this with a rather small team. Hell, there are even third-party Telegram clients that, while a bit behind the features, eventually catch up with every single one.

You don't get to be a billion dollar company by spending money unnecessarily. The question is never the total size of the company the cost relative to other options.