But doesn't decentralisation mean two thing?

One is the nodes, the other is the decision-making. Institutions like DARPA like the decentralised node structure for security reasons, somewhat like the internet itself was built to withstand nuclear attack. But I don't think DARPA would consider that the US Military decentralise their control structure.

The capped DPOS looked interesting until that paragraph that Members could delegate their stake thereby opening up Libra to complete central bank control by sheer weight of money - as well as making the capping pointless.