I don't think decentralized is meaningless, I think it has different meanings and interpretations.
Does decentralized refer to network topology, power dynamics, or both?
If we're talking about network topology, does it matter if different nodes in the network are owned by different entities?
If an architecture is in principle decentralized, but the current implementation has one or ore single points of failure, is it in fact decentralized?
If one layer of the system is decentralized (web, PDSs) but power is heavily concentrated in another layer (search engines, relays) is it a decentralized network?
If we're talking about equitable distribution of power, what kinds of power are we talking about, and how equitable does it have to be to be considered decentralized?
etc etc etc