When I saw this I actually laughed. But then I thought about it more. I’m actually inclined to agree with you, for a native API it is quite extensive, well documented, and fairly easy to use. I prefer its verbosity to Unix-style 6-character-long syscalls, though I can see why it made sense at the time it was developed. But it could just Stockholm syndrome after 5 years of use.
It's reliably stable. With a current Mac, running an app that was built 10+ years ago would be a nightmare if not impossible without source. With Windows, I can still run apps from the late 90's with little effort (with the exception of some DirectDraw issues).
I'm not really familiar with it, but I do know it went through a lot of revisions in the beginning when just about everything that could be exploited was.
So I would imagine it would be a time (battle?) tested, mature api.