I think the important concept that "readable and modular" is trying to get at is how easy is it to continue working on the code in future. There's definitely codebases that are easier to work on than others, even when the domain is the same.

I'd say that readability, which often boils down to consistency, and modularity are ways to do this, but they aren't the only ways. And as you say, sometimes there's a need for "unreadable" code, so not everything can be easy.