Can you name any such “reasonably-decentralized” proof-of-stake system or are you only thinking of proof-of-work variants
I'm not aware of any (confidently) reasonably decentralized proof of stake systems, however the non-delegated varieties are at least somewhat more decentralized since they lack a by-design centralization feature (for better or worse).
To claim DPoS is decentralized when one stakeholder is known to control 35% (i.e. far more than 19% vote received by the highest voted witness) of the of the voting stake is quite absurd. In other cases it might be unproven or unprovable but is at least less absurd on its face.