I don't think there will be any useful answers, fast or otherwise, until a definition of the term decentralized is settled on which incorporates a fundamental

I don't think there will be any useful answers, fast or otherwise, until a definition of the term decentralized is settled on which incorporates a fundamental requirement that the system so labeled be always tending toward greater decentralization by default, rather than (as most systems do, all blockchain projects included) tending to converge toward centralized leverage over time. the key seems to be that there has to exist, on the part of all members of the group seeking to collectively optimize their behaviors to foster some shared set of values, an established and non-negotiable priority of decentralization over (even at the expense of) every other value (cost, speed, personal gain). Inevitably this priority becomes compromised as decentralization is 1. a poorly defined value to start with and 2. accrues benefits that are local to the group but non-local to its individual participants. As the group grows this dilution of its value, manifest as an increasing remoteness to the interests of each individual it depends on for support, becomes a hindrance to its support vs., say, transaction speed or cost or personal gain. one of the very rare nontrivial examples of such a system would be the pre-capetian custom of equal division of estate inheritance in Merovingian France, vs. the primogeniture commonly practiced nearly everywhere else. And this too eventually succumbed to its own success, as the frankish state was "decentralized" due to this custom, its identity dematerialized and its integrity made vulnerable to regional rivals.