Unfortunately, “faithful and discreet slave” is a mistranslation. Playing devil’s advocate, the actual term is “faithful and wise servant.” Whether the term “faithful” can be used in connection with the Governing Body is moot. “Wise” is defined as “having wisdom or discernment for what is true, right, or lasting.” The term “discreet” is “exercising or showing prudence and wise self-restraint in speech and behavior.” And finally, a slave is “one bound in servitude as the property of a person or household,” where a “servant” is “one who is privately employed to perform domestic services.”
Now whether the Governing Body is a faithful and wise servant is something members of the Jehovah’s Witnesses must decide. But they also have to decide whether the GB is responsible for the horrendously awful translation of the scriptures.
You also quoted Revelation 22:18* to show that the translators shouldn’t have used “Jehovah” in their New Testament Greek translations. You wrote that “they did not remain faithful to the extant manuscripts.” As horrendous as the JW New World Translation is, a translation is merely to render into another language. If the GB is inspired of God, then making these changes is perfectly okay. Also, the scriptural reference to Revelation 22:18 refers only to the book of Revelation, and not to the Bible. The early Christians had an open canon. King James translators changed many references to God to “Lord.” This didn’t mean that they were adding to the scriptures, or taking away from them; nor did it mean that the translations were necessarily bad. But they are weighted to the JW doctrine where, for some insane reason, the term “Jehovah” is overly important to them. In most other faiths, Jesus is the one to whom Christians look. And the JWs believe that Jehovah is the Father of Jesus where the scriptures teach fairly clearly that Jehovah, not Michael, is the pre-existent Jesus.** If the GB is wrong about that, then that’s another doctrinal kink they have to answer for.
--------------------- * “For I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto these things, God shall add unto him the plagues that are written in this book….”
** Both Jehovah and Jesus share the same titles, such as the First and the Last, Savior, Judge, etc. In fact, Jehovah will come to judge the nations, and his coming mirrors that of Christ’s. John declared that the Father judges no man, but has committed all judgment to the Son. (John 5:22) The Witnesses explain the identical titles by saying that Jesus is so much “One” with Jehovah that they can use the same titles.