I feel that there is a sense in which you could be right. The city of Colossae in Asia Minor, some 170 kms from Ephesus was a trading and commercial centre based on the rich mineral deposits in the Lycus Valley, where this city was. There would have been a good mixture of Jews and Gentiles in the local church, to which Paul wrote his letter.
In verse 27 of chapter one of this letter, Paul specifically mentions the "mystery" of the Universal Church which was being revealed at that time among the Gentiles, which "mystery" was that Christ was in "you" - the Gentiles - his readers. So there is no doubt that there were Gentiles in the local community and they woud have read Paul's letter.
Also, in verses 11 and 13 of ch 2 he refers to his readers as having an "uncircumcision" of the flesh, and that their "circumcision" was indeed one "not made with hands'' So it seems quite likely that he was adressing the Gentiles in the church with his letter, but he would have included as well those who were former Jews and who had now come to be "in Christ"
The purpose of this letter was not adressing the distinction between the two groups making up the Church community of Colossae, but was attempting to allay a threat that was trying to outflank the Christians in Colossae. The threat of Gnosticism. This was a seminal belief system of various theosophies which contained several abstractions, including the need to take in an exclusivist form of knowledge [gnosis] from a tightly controlled centre. This germination of a heresy was clearly denying the Deity, hence supremacy, of Christ, thus calling for one of the greatest declarations of the Deity of Christ found in all Bible literature [1:15 - 2:9]
Evidently the Jewish element were counteracting this incremental influence of gnosticism by a reliance on the Mosaic Law, and may have tried to influence the Gentile believers in this way of thinking. Paul showed his readers at Colossae, both Jew and Gentile, that neither the Law, nor Gnosticism was the answer. The Answer was Christ, personally. The injunction of 2:16, 17, may certainly have made reference to the Law, but that was not the only concern of Paul. Remember at verse 18 he mentions the "worship of angels'' and "delighting in self-mortification" - NEB, as elements of this same injunction, which were prominent gnostic dogmas. So yes, both, Jews and Gentiles would have been included in 2:16-17. While the Jewish element was influencing the Gentiles so also the Gnostic element was trying to influence both groups, hence the statement at 2:16,17.
It is pathetic that the WTS and its followers have to resrict the contextual reference of this injunction, not because of its biblical implications, but to support their own untenable position.
Cheers