I think a lot of this disagreement could be cleared up by using “hallway usability testing”. The test is simple: Grab the next 6-8 people who walk past your desk and say “hey do you have 5 minutes to test the usability of something?”. Ask them to do a series of actions with the application (change to a list view, go up one level in the directory hierarchy, etc). Take note of what they find easy and what they struggle to do.

I suspect that I would struggle in many of the same points as the author. I suspect many other people would as well.

If you think this UI is good, do you want to make an objective claim? Do you think 8/8 people who walk past would figure out that split drop down button? It is very easy to test.

Yes this stuff is subjective. But rules and principles fall out pretty naturally from just asking people to try out your interfaces.