- Zbrush has an extensive ecosystem of bushes. There are specific tools for specific jobs, and (not having used Blender at all) I am skeptical Blender successfully replicated these workflows.
- Zbrush has modes that are extremely precise. For example, you can mask off a specific section of the mesh, similar to masking off a portion of an image in Photoshop. Except, in Zbrush, you can do it spatially -- it's not a "mask per triangle", but rather "a mask per pixel". You can literally slice a mesh in half, vertically, screen-wise, then hide one half, do some work on the other, then un-hide. It's an effortless flow that people use all the time.
- Zbrush is most natural to use with a tablet in one hand and a keyboard in the other. That video isn't using a tablet at all. Having a mouse interface just isn't appealing for artists. The reason I bring up this point, is because I can't overstate how natural it feels to use zbrush with a tablet –– you can bring up a "context menu" just by tapping a button on your pen, select a new tool by flicking your wrist slightly, and immediately begin using that tool. It's far more configurable than I'm describing here.
Ultimately, Blender has to serve too many masters. If you have to design a UI that can do anything, it can't do everything well. It must make tradeoffs. And these tradeoffs are reflected as reduced artist productivity, which is why many artists use Zbrush for their professional work – it's a tailored experience specifically for artists.
Now, all that said, I am impressed with what Blender can do. I like that it's open source. But, if you want to go toe-to-toe with the pros, the pros are going to point out exactly why the interfaces just don't cut it. If it takes 20% longer to accomplish X, those small costs add up. But there's also a "step change" that you get from the Zbrush flow that I don't think you'll get with Blender's interface. It's subtle, hard to describe, and honestly something you'd have to invest time in to understand.
Caveat: I've been out of the art world for around five years at this point, so feel free to ignore all of my points. But, I approach this from a gamedev studio mentality: from experience in the industry, I can say that Blender never once came up as a realistic option. It was 3ds max for a long time, then mudbox pioneered the sculpting concept (I remember Aron Zoellner from my first job going on and on about why Mudbox was so cool and a big deal), and then Zbrush totally dominated the scene. There are reasons for this, despite my inability to perfectly articulate them.
Scrub through https://youtu.be/EdEVj39ur-U?t=1545 and watch how effortless everything is. That artist is doing so many operations per second relative to your Blender video that it's hard to overstate just how much more productive they are. (I realize your video was an introductory example for Blender, but it's hard to imagine someone doing in Blender what that person is doing in Zbrush.)