Ousterhout's core argument is this: consider a module as its interface (measured, say, in # of edge cases) multiplied by its effect (measured, say, in # of features achieved). When comparing two modules, we should prefer modules with smaller interfaces and larger implementations, i.e. of two modules with equally sized interfaces, prefer the one which does more, and of two modules which do the same thing, choose the one with the simpler interface.

Narrow vs wide in this context seems to me to mainly be a point of comparison - in practice, narrow and wide don't make much sense when talking about a module on its own, because the dimensions of interface and implementation are not comparable.

However, this article seems to mainly be about comparing interface to implementation and arguing that, because interfaces can be very complex, often as complex or more as the implementation itself, then Ousterhout is wrong. Or in other words, if we convert "# of edge cases" and "# of features achieved" to a single comparable unit like "# of lines of code", then for Ousterhout's advice to hold, then the implementation must be more lines of code than the interface.

To me, that's kind of missing the point of the advice, which is less to do with the amount of code needed to implement something, and more to do with the capability of code vs its interface. Yes, lines of code can be a useful proxy for both dimensions, but the dimensions aren't meant to be directly comparable.

I might be missing something, though.