pg_createsubscriber is currently grouped as a Server Application:
https://www.postgresql.org/docs/devel/reference-server.html
Contrast the list of Client Applications:
https://www.postgresql.org/docs/devel/reference-client.html
Note that the latter includes pg_basebackup, pg_receivewal, and
pg_recvlogical, which feel generally similar to pg_createsubscriber.
My mental model for Server Applications is "does not make a remote libpq
connection", which does not match what pg_createsubscriber does.
(An indirect effect of this grouping is how packagers split their
-client and -server packages. There are currently a number of
discrepancies among popular packagings, including this one. (I know
that moving files between packages is sometimes difficult, and I don't
necessarily expect that packagers would immediately move this, but at
least the directional guidance could be made more correct.))
