The thought occurs that it's not so black and white because functionality changes depending on what you're observing and from where.
For example, you might argue that removal of a minor node would have no discernible impact on the overall system, but it would have a critical impact on the few users of that node.
I've long said that Fediverse isn't so much decentralized as re-centralized around instances. So I guess that's what people mean by federated instead of decentralized.
It seems like Bluesky addresses this better, being more decentralized in terms of not being reliant on instances.