> not really an OS, just a super-fast way of dealing with I/O streams
Saying this without any animosity, but you would probably be interested in reading about the history of operating systems. Desktop OSes are a (very visible) minority, and it's the opposite way in my opinion: a desktop OS is an OS + a large suite of tools + a shell.
It's literally something that operates the system so that every program written doesn't have to handle all the low level IO, that enables task management, etc.