I gotchu and I understand what you mean, just assisting with clarity because it is more fair to say "Mac OS X has continued the lineage of NeXTSTEP" than it is

I gotchu and I understand what you mean, just assisting with clarity because it is more fair to say "Mac OS X has continued the lineage of NeXTSTEP" than it is to say "Mac OS X is basically NeXTSTEP." Think about everything Mac OS X has or has had which NeXTSTEP has never had. DTrace, HFS+ and then APFS, Quartz replaced Display PostScript, OpenGL and Metal, IOKit replaced DriverKit and is now being functionally replaced (at least in part) by something called Driver Kit, Catalyst, SwiftUI, Quick Look, Spotlight, Safari/WebKit, Keychain, Xcode has replaced both Project Builder and Interface Builder, Core Audio, Core Animation, QuickTime and then QTKit and then AVFoundation, I mean the list goes on. Unicode is everywhere now too, which is neat; NeXTSTEP and Mac OS had their own character encodings. Carbon was also a significant technology for the first few years, as was the first Rosetta (and we have Rosetta 2 now), and the Classic environment. So, clarifying more than disagreeing. :)