Exactly. The core that was open-source, but not FOSS per FSF, is a system almost no Mac user will directly use or develop apps for. The experience Mac users get

Exactly. The core that was open-source, but not FOSS per FSF, is a system almost no Mac user will directly use or develop apps for. The experience Mac users get is almost totally proprietary by Apple. It's not only theirs in copyright: they patent every aspect they can to sue anyone doing something similar. Samsung will happily attest to that. Mac OS is about as non-FOSS as it gets. Right up there with Windows on proprietary components, lock-in, and patent suits by owner. At least they're doing a nice, open-source project with LLVM. I'll give them credit where it's due.