Things exist on a spectrum. I have autonomy to choose where to (e.g.) host my family photos, and even self-host on a VPS or even perhaps at home (either with a static IP or dynamic DNS). While things may moved towards more centralization with Big Tech, does not mean it is centralized, just perhaps less decentralized / distributed.

> multiple centralized systems

This phrase approaches an oxymoron in my mind. (Bearing in mind de/centralization being on a spectrum.)

Autonomy is the ease with which people are free to move between those governments.

I suspect people view the web as decentralized because they cannot divorce their thinking from concepts like content is king and a client/server model.

But you wouldn't say that the governing of Earth in total is centralized (e.g., the UN (with their black helicopters/s)).

Going back to my link:

> As its name implies, decentralized systems don’t have one central owner. Instead, they use multiple central owners, each of which usually stores a copy of the resources users can access.

> A decentralized system can be just as vulnerable to crashes as a centralized one. However, it is by design more tolerant to faults. That’s because when one or more central owners or servers fail, the others can continue to provide data access to users.

* https://berty.tech/blog/decentralized-distributed-centralize...

Or Baran (1964):

> For example, type (b) in Fig. 1 shows the hierarchical structure of a set of stars connected to the form of a larger star with an additional link forming a loop. Such a network is sometimes called a "decentralized" network, because complete reliance upon a single point is not always required.

* https://www.rand.org/content/dam/rand/pubs/research_memorand...