Earlier quoted context omitted.
Your link is discussing the development of Unix, which was before Rob Pike came on the scene. Rob Pike is discussing an incident that happened a number of years later when Rob would have been significantly junior to Ken. There is no reason that both versions of history can't be true.
On top of that, things would have grown in complexity since the early days.
Don't kid yourself. Systems may be larger and seemingly more complex, the individual parts are as simple or complex as they ever were. Anyway, if things are more complex the necessity of thinking it through are even greater.