Zooko's Triangle was a useful lens, but I think of it has having long been solved (or, refuted) by many blockchain projects.
The real answer to Zooko's Triangle is to do human-meaningful name lookups as little as possible. For instance, in an ideal world I should be able to run a nameserver that stuffs all of ICANN's TLD pollution under an .icann label, such that I could type "blog.google.icann" to access what is currently called "blog.google". References to other resources would be specified with decentralized non-human-readable (ie cryptographic) identifiers, and outgoing links intended for human consumption would also have a relative hint so that my browser could turn the cryptographic identifier back into a human readable identifier in my own namespace.
In the case of a naming system, as you point out, that means there is still one finite, scarce namespace in the system, just as there is in DNS.
More generally, there is still a central authority pushing out code, and so unless you want to hard-fork, what does the "decentralization" in a blockchain actually buy you? Does it do anything more for you in practical terms than protecting you from a central server suffering an outage?
I spent some time a while back coming up with ideas for an alternative to blockchains that would pursue many of the same goals, starting from first principles ("what the heck even _is_ money?"). I have no idea whether any of my ideas would have actually worked in practice, but they at least ticked the "decentralized" box in a way that I found a lot more meaningful than merely "decentralized execution of a centrally-defined algorithm to determine a single global consensus state". (I stopped working on them not because they didn't show promise, but because I became convinced that they would be a net negative for the world if they were successful; I lost the desire to find a working design.)
Not necessarily, it's quite common for forks to compete on a single ledger, with features activated when the majority of miners elect to run the fork which supports them.
I'll use bitcoin as an example. If you are using visa/mastercard, they can censor you. The government can order them to censor you. Bitcoin mitigates this problem. If a particular miner refuses your transaction, you have plenty of other miners to choose from.
I think about the only decentralized improvement one can do is software that creates credit lines denominated in an existing currency, between mutually trusting parties. And then attempt to scale that up (ala Hawala), with technical means to keep the slightly diminishing fungibility from being an issue (one USD owed to you by the Treasury is worth slightly more than one USD owed to you by your friend A (owed to him by B, and so-on), even if you trust A with your life).
However, there are many areas where we can adopt decentralized functionality (which actually means not having unnecessary centralized functionality), such as my above naming example. If we want decentralization, it's just ridiculous for my browser to be making hundreds of centralized name lookups to render a single page. And I've seen too many blockchain projects where they're actually pushing a solution that is more centralized than the existing ones.
furthermore, I heavily doubt it's even a realistic argument that a single high net worth individual could ever compete with a globally sized competition where it's easy to vote via: 1 cpu = 1 vote mechanism. it would be much easier with the traditional asics mining because the high net worth individual could have the money and means to buy up all the asics or produce them himself, but with the ease of availability of cpus, I heavily doubt that it's the same ball game.