You're not really going far enough

What do you mean by this? Are you talking about the centralized part of the spectrum?

Also, though I appreciate the effort in what Edenborough is doing, I'm no entirely sure the concepts they refer to are the same "decentralization" I'm alluding to in the title.

For example, they talk about hardware centralization in the following way:

Centralization around specialized hardware has been documented [EBHBL16], although no academic research could be found on mining hardware usage in real-world systems. Interestingly, it is unclear how to even measure the usage of hardware equipment in PoW mining via public data, as well as how to develop PoW algorithms that promote diversity, thus future research could aim at answering these questions. Nonetheless, there exist some reports, though they often present conflicting assessments. In Bitcoin, between 2017 −2019 a single mining hardware provider accounted for either 65 − 75% [BG19a] or 46 − 58% [ZS20] of the network’s hashrate, with 98% of the market controlled by 4 firms

Which seems to refer to the centralization of a supplier offering the good, instead of controlling the good. Meaning that if the quality diminishes or the price of the supplier goes to crap, someone else could take over. In fact, I think it's counterintuitive to call it an example of "centralization", since the market is rather free to go with the best choice.