Since there's no agreement on whether PoW is essential (many might not even know an alternative), two sides arguing about things might actually be arguing about *different things*, thus "shouting past each other", which we do see on here all the time.
I think there's a good "shape" for what we might call a blockchain, but before we get to that, let's get to the other big argument that's happening on here: "blockchains" as an identity space... and a proxy war for other cultural dynamics!
Side note: NFTs are not copyright, and actually I don't even think copyright (which bottoms out in state violence) is even a good *idea*, but people are being sold something which isn't what they're getting, and it's no wonder that people are mad about it.
Almost all the focus of decentralization is in the "decentralized convergence", or sometimes if i'm smug, the "decentralized centralization" space. This is the world of blockchains and "quorums" (we'll come back to that)
However, most of the *important work* that needs to be done doesn't require a ledger, it's in the "decentralized cooperating agents" space. This is the realm of ActivityPub, the "actor model", and distributed capability-secure programming (CapTP!)
So: are blockchains essential to decentralization?
No! In fact, decentralized approaches dramatically predate Bitcoin! In fact, blockchains often lead to "reproducing" centralized structures because it's just too easy to "throw the centralized mindset on top of a blockchain"!
What if "blockchain" just meant "a single machine that many people run"?
The idea here is that a blockchain isn't a bunch of decentralized machines... it's a bunch of machines building *one unified abstract machine*. Useful for decentralized agreement on sequential operations.
Except we might actually want to split this up: there are "public" blockchains, like Bitcoin, Etherium, ZCash, and then there are smaller intentionally assembled sets where "here are the five participating machines, if three out of five agree this is the next action, then it is"