MacOS is not a fork of BSD but uses some of its use land. I think it’s considered a BSD because of that, but the kernel and graphics libraries are all Apple.
The kernel isn't all Apple, it's a fork of the open-source Mach kernel developed at CMU (which was a replacement BSD kernel). "Ground up" just isn't real!
The graphics libraries are definitely more custom... Although in total fairness they're not entirely ground-up Apple either; Quartz was based on Display PostScript, which was acquired from NeXT, and which NeXT built in collaboration with Adobe based on Adobe's earlier work on PostScript. It's obviously true Apple's done a lot of work since then (e.g. Metal), but in that case, so has Google since forking Webkit.
Quartz isn't based on DPS - CoreGraphics drawing commands are similar to PDF but the window management was always all pixel based - and IIRC DPS was almost all Adobe and NeXT didn't even have source for it.
The graphics libraries are definitely more custom... Although in total fairness they're not entirely ground-up Apple either; Quartz was based on Display PostScript, which was acquired from NeXT, and which NeXT built in collaboration with Adobe based on Adobe's earlier work on PostScript. It's obviously true Apple's done a lot of work since then (e.g. Metal), but in that case, so has Google since forking Webkit.