Docker has documentation and user interface that is at least several orders of magnitude clearer, and it is much faster and easier to learn (no obtuse, undocumented, unique syntax) and is generally well-integrated (that is, people don't get confused when a repository has Dockerfile, they know what to do with it)
Because you don't want to learn anything new, you're going to ignore the clear advantages and demonstrable benefits of it then? Fair enough. I'm not going to argue with cognitive dissonance like that.
I think what they're trying to say (with some artistic depiction from my side), is that Docker, which is much more intuitive and easy to use, which "does one thing and does it well", is ultimately superior to Nix in the containers space, even with the minimal advantages that Nix has over Docker. Especially for large-scale production scenarios, where in those cases, k8s is used more commonly with Docker.
So the only disadvantage of Nix is the learning curve? I'll take it! I wouldn't call the advantages minimal though, it's quite clearly demonstrated that the implications for supply chain security are massive to say the least. Blindly following what people are "commmonly using" won't get you anywhere good either.
In my opinion, yes. I think really the biggest disadvantage you have with Nix is the learning curve. I mean the language is horrendous but I don't think it's really that much of a disadvantage neither.