The faithful and discreet slave is just an illustration like the rest mentioned. It is not partial prophetic. Besides nowhere does it say to obey this slave.
Jesus specifically commanded us to avoid following men who would lord it over the congregation, such ones who desired to be called by special titles and be treated like kings.
The "special full-time servant" arrangement (including the Bethel commune, the COs, the Governing Body, etc) is in opposition to Jesus' teachings as revealed through the apostle Paul. Jesus doesn't want us to follow such men. He wants us to avoid them.