Yeah, 100%. At this point the resources invested in MacOS / iOS have probably exceeded even the decades of work they were able to leverage by starting with FreeBSD / NeXT / Mach / whatever else.
(Edit: Actually, not 100% true. Macs are still very BSD-like under the hood; I actually really like development on Macs because I can basically treat them as BSD systems with unusual package management and a fancy GUI. For that reason they’re far preferable for me over Windows or pre-OSX Macs. But yes, your point is well taken that iOS development at this point has far eclipsed anything they started out from in terms of LOC and time spent.)