Jehovah's Witnesses' publications address your question in numerous places.
Your assertion that Colossians 2:9 means that Jesus is God is a dogmatic statement that Trinitarians frequently use.
However, theotes is just as capable of expressing quality as it is identity.
See the extensive reasoning at "The Fullness of the Divine Quality" in Colossians 2:9.
In part that site states about the words used in KJV and other bibles to translate theotes:
Straight away, two things should be apparent: Firstly, none of the above-mentioned words - Godhead, deity, divinity - necessarily mean that Christ is Almighty God. True, they could all be interpreted to mean that. But, then again, they can all be used to mean having the nature of a god rather than Almighty God. Secondly, all of these terms refer first and foremost to character, quality, state, nature and then, by extension, to identity.
Additionally, you can look at official JW reasons for how Colossians 2:9 is rendered:
Colossians 2:9 NWT
because it is in him that all the fullness of the divine quality dwells bodily.
Like John 1:1, Colossians 2:9 references the qualities of the son of God. Jehovah's Witnesses are in agreement with translations of John 1:1 that say “the Word was Divine.”
Specific commentary on the verse in question is found in Reasoning from the Scriptures:
KJ reads: “In him [Christ] dwelleth all the fulness of the Godhead [Greek, the·oʹte·tos] bodily.” (A similar thought is conveyed by the renderings in NE, RS, JB, NAB, Dy.) However, NW reads: “It is in him that all the fullness of the divine quality dwells bodily.” (AT, We, and CKW read “God’s nature,” instead of “Godhead.” Compare 2 Peter 1:4.)
Admittedly, not everyone offers the same interpretation of Colossians 2:9. But what is in agreement with the rest of the inspired letter to the Colossians? Did Christ have in himself something that is his because he is God, part of a Trinity? Or is “the fullness” that dwells in him something that became his because of the decision of someone else? Colossians 1:19 (KJ, Dy) says that all fullness dwelt in Christ because it “pleased the Father” for this to be the case. NE says it was “by God’s own choice.”
Consider the immediate context of Colossians 2:9: In verse 8, readers are warned against being misled by those who advocate philosophy and human traditions. They are also told that in Christ “are hid all the treasures of wisdom and knowledge” and are urged to “live in him” and to be “rooted and built up in him and established in the faith.” (Verses 3, 6, 7) It is in him, and not in the originators or the teachers of human philosophy, that a certain precious “fulness” dwells. Was the apostle Paul there saying that the “fulness” that was in Christ made Christ God himself? Not according to Colossians 3:1, where Christ is said to be “seated at the right hand of God.”—See KJ, Dy, TEV, NAB.
According to Liddell and Scott’s Greek-English Lexicon, the·oʹtes (the nominative form, from which the·oʹte·tos is derived) means “divinity, divine nature.” (Oxford, 1968, p. 792) Being truly “divinity,” or of “divine nature,” does not make Jesus as the Son of God coequal and coeternal with the Father, any more than the fact that all humans share “humanity” or “human nature” makes them coequal or all the same age.