So I think Steve's attitude has to be put into the context of that conflict. But as MrTonyD shows, there were people at NEXT who understood how to translate that attitude into practical terms. And to be fair to Steve that's because he knew how to hire absolutely tip-top talent and trust them to do their jobs right, even when they disagreed with him.
I don't really see that they were wrong. After all, C and POSIX are also very high level and abstracted compared to the assembler-based OSes which existed before them.
The big problem now is that to be a successful alternate OS one needs to be bug-for-bug compatible with POSIX, and have a C compiler, in addition to one's own language and OS. Perhaps recent years' developments in virtualisation and containerisation will make it easier for a non-Linux host to run a Linux kernel and hand containers to it as needed.
Maybe one day OS and systems research will once again pay off.