I don't think your "spirit medium" analogy holds up well. After all, Jesus Christ said, "I am the way, the truth and the life. No one comes to the Father except by me." Does this mean that those who asked Jesus for God's view of things were consulting a "spirit medium?" The fact is, the Pope also claims to serve as God's spokesman in much the same way as the leaders of the Watchtower do. However, I believe nearly a billion Catholics would highly object to the assertion that they are consulting a "spirit medium" when seeking the Pope's guidance in spiritual matters.
I do not believe that either the Watchtower Society or the Pope can fairly be accused of acting as "spirit mediums" for claiming to receive special revelations from God. If they could, then all of the Bible's writers and all of God's prophets from the times of both the Old and New Testaments, could also be fairly referred to as "spirit mediums." But I believe such characterizations would be unfair. Why? Because a "spirit medium" is defined as someone who claims to be able to communicate with the spirits of dead humans.
With this said, please don't get the idea that I am defending the Watchtower Society in this area. Quite the opposite in fact. For the fact of the matter is, the leaders of Watchtower have long claimed to be in communication with the spirits of dead humans. And because they have, I believe it can fairly be said that they are claiming to be acting as "spirit mediums."
When have they claimed to be in communication with dead humans? Though I don't have the quotes at my fingertips right now, I believe they have made this claim several times in the past, when they have said that their work was being directed by members of their sect who had already died and been resurrected to heaven. For many years the Society taught that the heavenly resurrection began in the year 1878. As I recall, it was with this in mind, that J.F. Rutherford, the Society's second President, taught that his writing work was being guided by the resurrected spirit of the Society's first President, Charles Russell. In more recent years the Society has taught that the heavenly resurrection began in the year 1918, but their teaching that they are somehow communicating with the spirits of dead JWs continues.
In the book Revelation - Its Grand Climax At Hand, (published in 1988 but carefully studied by all JWs in their midweek book studies just this past year) it was written, "This suggests that resurrected ones of the 24-elders group may be involved in communicating divine truths today." ( page 125, paragraph 17)
So, though I differ with you on the way in which you reached your conclusion, I agree with that conclusion. The Governing Body of Jehovah's Witnesses do in fact claim to be acting as spirit mediums and all Jehovah's Witnesses who seek their direction on spiritual matters can, I believe, be fairly said to be "consulting spirit mediums."
