This seems to still rely on (or at least, describes) the client making the determination of what to talk to, not the mesh / service discovery.

Well, it does exactly what op wrote: "your client retrieves a subset of the available instances via service discovery, establishes connections to every instance in the subset, and spreads requests between them"

The article you linked describes retrieving all instances and establishing connections to a subset of them, not retrieving a subset of them. To achieve deterministic apertures it further needs both the complete serverset and the complete peerset.