That might be what OS'es currently _are_, but I disagree that it is what an OS _is_. I think fundamentally an OS is as the OP uses it, a set of code that interfaces with all your hardware to make the computer function.

Heres a good talk I came across in a HN comment a little while back [1] about how games used to be developed vs how they are today.

[1] - https://www.youtube.com/watch?v=kZRE7HIO3vk