The JWs reject the label of "polytheist", yet they say Jesus was not a mere human. They say he is "a god" or "divine".
Not exactly. They also say he was nothing more than a man, albeit perfect, which would create another contradiction if they also consider him a god. Hence they dilute "a god" to really mean god-like or divine to circumvent the polytheistic implications. Either way they are patently wrong. More here:
"Jesus, no more and no less than a perfect human, ... " (Should You Believe, Chapter 6)
The Arian Heresy - The Jehovah's Witnesses teach 4th century Arian Subordinationism, an early heresy condemned at Nicaea I.
Most Jehovah's Witnesses are unaware that their conception of Christ is an adaptation and resurrection of 4th century Arian Subordinationism and theories propounded by earlier Ebionite heretics (Catholic Encyclopedia, 919). In 318, Arius, a priest of Baucalis, propounded the doctrine that Christ is not fully divine (Oxford, 1209; Encyclopedia of Religion, 54). “Arius asserted that the Son was a perfect creature, at most a kind of demigod subordinated to the Father” (Encyclopedia of Religion, 20).
The Father alone, Arius argued, … is ungenerate, source without source, self-existent. Therefore the Father alone is truly eternal…. (Catholic Encyclopedia, 297)
“Jesus must be a creature, albeit one who was exalted and achieved union with God. … Arius insisted ‘there was when he was not.’ Arius was simply fulfilling the Stoic-shaped logic of trinitarian reflection prior to Origen, for he assumed that the expressed word of God (the Son) was inferior to the inherent reason of God (the Father). (Oxford, 1209)
Subordinationism suggests “… that the Father is somehow prior to the Son and the Spirit. … It was this tendency, pursued by Arius and others, which the Nicaene and Constantinopolitan creeds set out to avoid. (Oxford, 1211)
“Arius conceded that Christ was divine; but only in a translated figurative sense of the term. In other words, He is not literally divine at all. He is the most exalted of God’s creatures, authorized by God to be His agent in the work of creation, and adopted as His Son. The Word, then, was specifically different from the Father. He is a secondary deity, subordinate in nature to, not the equal of the Father …. From Arius’ viewpoint, Christ’s coming signifies nothing more noteworthy than the arrival of another creature, the decent of a demiurge into flesh” (Catholic Encyclopedia, 919).
Semi-Arianism taught that Jesus Christ is a god subordinate to the Father, which is precisely what the Jehovah's Witnesses teach as reflected in their translation of John 1:1, “And the Word was a god” (NWT), not the “God” of mainstream Christianity.
With minor modifications, the similarities between Arianism and the Jehovah's Witnesses’ theory on the nature of Christ are striking. Their conception of Christ is not a unique revelation by the society’s founder Charles Taze Russell but reaches back 1,600 years to the first centuries. The Jehovah's Witnesses teach:
Jesus, (was) no more and no less than a perfect human. (Should You Believe, Chapter 6)
Jesus was a created spirit being …. Having been created by God, Jesus is in a secondary position in time, power, and knowledge. (ibid.)
(God) created the prehuman Jesus directly. Thus, Jesus had a beginning and could never be coequal with God in power and eternity. (ibid.)
Not only is Almighty God, Jehovah, a personality separate from Jesus but He is at all times his superior. Jesus is always presented as separate and lesser, …. (Should You Believe, Chapter 8).
In every period of his existence, whether in heaven or on earth, his speech and conduct reflect subordination to God. God is always the superior, Jesus the lesser one who was created by God. (Should You Believe, Chapter 7). Taken from http://144000.110mb.com/trinity/index-8.html#41