I "liked" Opus dei's comment on the salad of beliefs in the first century.
I would say we should make a distinction between christianity, alias the historical christ cults before Jesus, and the Jesus christ-cult which was derived from them and became orthodox western Christianity under Roman patronage in the fourth century CE.
It was the Roman Christ cult which stuck the new name of a composite pagan and Hebrew saviour god-man "Jesus" to that role. This name, although it resembles half a dozen other names in a number of languages, has a common denominator in the Latinised symbol of the sun: the letters IHS, both in Hebrew and the the Greek. "Iasus" was one of the names assumed by initiates to the Dionysian christ cult well before Jesus. Remembering that in English, the letter "J" began as a capital "I". (This is just the tip of the iceberg on the pagan origins of Christianity and I will refrain here from going further!)
Perry you ask a good and reasonable question but you are only looking to an interpretation of the Bible for an answer, that is like digging for diamonds only in your back garden. The meanings and answers to problems of human culture and whether JWs are Christian are found much more readily and with greater certainty outside of the Bible.
Seen through an anthropological lens, JW are followers of Christ Jesus, hence they are Christian... and their religion comes from Adventism and before that protestantism, before that the Roman Catholic Church and before that the second century fusion of christ cults, before that it was drawn from cabalistic sun worship and before that astrological folklore.
If you are seeking to condemn JWs as unchristian you are using the same unreliable straight-edge which measures all who today call themselves Christian.