Windows NT and MacOSX are both scratch rewrites. Though the author of the comment may be referring to the fact that Android and iOS dominate the space now.

No no, I referred to your point precisely: both Win and Macos had to be rewritten from scratch at some point.

> macOS died

Classic Mac OS died, and what they call "Mac OS" now is really NeXTSTEP.

“Death” seems a bit dramatic in this context.

> “Death” seems a bit dramatic in this context.

Classic Mac OS is about as dead as software can get: it's no longer developed or developed for, there's no backwards compatibility in its successors, and they don't even make hardware that can run it anymore.

Apple would disagree

https://www.youtube.com/watch?v=Cl7xQ8i3fc0