What changed
Cosmos: many chains, and no one chain's security covers the rest.
The paper's point is interoperability without forcing every application onto one validator set. The cost is that a weak zone is not saved by the hub.
Original thesis
Zones run their own consensus. A hub routes packets. The inter-blockchain communication protocol is the seam, not a shared court for every execution.
What changed
Live networks added light-client assumptions, relayers, and application chains that look more like products than zones in a paper. A halt on one chain does not halt the others. It also does not get their security.
What remains useful
Use this when a design claims 'sovereign but connected'. Ask who validates the zone, and what a packet means if that set stalls.