Is the namespace decentralized? That depends on how you use it. If you use GNS with an ICANN provided root zone configuration (this is an example, there is no such thing atm), then your names will have the same meaning as for other people using this configuratin. If you build your root zone from scratch, you will have modified the namespace in such a way that names are no longer unique. If you go full petname system (ie. names are basically treated as your personal address book), the names are no longer unique.
Think about DNS: If you are sufficiently technically literate, you can run your own root servers and use them. Is DNS at odds with Zookos triange? I would argue: Yes, depending on how you use it. It is just very common to use it with unique global names.