I think you should substitute “code” for “domain” in the last paragraph.

John Carmack knows his domain very well. He knows what he expects to see. The debugger gives him insight into what “other” developers are doing without having to modify their code.

For Carmack, managing the code of others the debug environment is their safe space. For Kernighan et al in the role of progenitorous developer it is the code itself that is the safe space.