Some possible answers:
1) Justification due to the large number of followers.
False. There is less than one JW per one thousand persons. Equally telling is any comparison of membership numbers of the WTBTS and any mainstream religion.
2) Justification due to large growth.
False. There is zero or negative growth in nearly all first and second world countries. As far as total growth goes, for every additional JW last year, there were about 150 additional Catholics and perhaps the same number of Protestants.
3) Justification due to worldwide scope of the preaching effort.
False. In every country where the WTBTS has a presence, it is usually well down on the list when ranked by number of members or new converts when compared to other religions. Also false because of the resistance of the WTBTS to actually PAY for media usage (radio, television, newspapers, etc.) and being more interested in extracting money from new territory than spending it there. A few hundred total Gilead missionaries is a small drop in a big bucket when compared to the evangelization efforts of other religions.
4) Justification due to singularly proclaiming God's name.
False, on three accounts. First, there are other religions that have no problem with discussing God's name. Second, "Jehovah" isn't even close to "Yahweh". Third, and most important, it's not God's personal name as much as it's God's LAW (Greek _nomos_), as in the expression "In the name of God" meaning "By the divine law".
5) Justification due to succession from the first century.
False. Charles Russell had no predecessor, either an individual or an organization. Various persons' names from the past two thousand years put forth by the WTBTS (Arius, Wycliffe, Luther, etc.) all had far more in common with each other than with the WTBTS.
6) Justification due to success in interpreting prophecy and making predictions.
False. Need I mention anything about 1874, 1914, 1918, 1925, and 1975?
7) Justification due to accurately discerning the "deep things" of the bible.
False. A mountain of doctrinal flip flops proves otherwise.
8) Justification due to following biblical precepts.
False. What about feeding the hungry, giving water to the thirsty, of healing those who are sick?
9) Justification due to exemplerary good conduct of its members.
False. I'm not going to even touch this one.
I would hope that there would be at least a couple of real JWs who would try to answer the original question about the WTBTS claim of being "spirit-directed". You JWs spend many hundreds of hours a year going to meetings and banging on doors. But if you can't answer the question, then you must admit to yourselves that you're wasting your time and that it's all a big fraud.