Adding onto this; the parts of the kernel that were from FreeBSD were taken two decades ago, without much if any attempt to follow up and rebase. I don't know about the disk I/O subsystem, or even if it was taken from FreeBSD, but the 2000 era FreeBSD tcp was scalable for 2000 era machines (although it would have been nice if Apple had taken it after syncache/syncookies), but needs changes from the 2010s to work well with modern machines. I'm sure that similar improvements have happened for disk I/O, but I just don't know the details. Not a lot of people would run a FreeBSD 4.x kernel today, but that's what's happening with the FreeBSD derived kernel bits in Mac OS.

The funny part about this is I actually end up installing a lot of the GNU tools so I can have some level of parity when writing (mostly shell) code on MacOS.