The thing is, you're talking about very specific examples. My point is that especially in UX design you can't use absolutes like that, such as "whitespace is always bad" or "whitespace is always good". This was also the author's point and this idea that "instead of whitespace we should use lines", "instead of whitespace we should pack things tighter" and so on is absurd.
Now here's UX Myth #35: "Modern UIs have good, established UX". Desktop, web, most everything I've seen are UX disasters blindly following trends. And just because you throw UX designers at a problem doesn't mean they will do a good job at it.
UX design is very much a "fake it till you make it" industry. It's based on good principles and mostly the scientific method, but it has a lot of reproducibility issues because it deals with a lot of subjectiveness. Also, some good UX principles may not apply in all situations.
And think about this: Most people are actually bad at their job. The majority of devs and web designers aren't working at Google/Facebook, they're making awful wordpress sites. This is less visible in UX design but it's still true - the majority of UX devs aren't good.
If you want a delimiter then use a delimiter, perhaps a line? One of my main gripes with "modern" UI are UI elements which have no defined border on them. For example, how do I know where's the border between two buttons, or whether there's any inactive space between them, when I see only text separated by whitespace (or for that matter, whether they're buttons at all or just text labels, which I argue should have no border)? It's quite disorienting.