Paul was not "anti-Sabbath" at all. He simply made it clear that under the New Covenant, Sabbath-keeping, as well as all the feasts, festivals, holy days, and ceremonial observances under the Law of Moses (including circumcision), were not applicable to Christians, particularly Gentile Christians. However, in those days, if Hebrew Christians still felt they should observe these things, they were told to regard them as "shadows" since the reality was (and is) Christ.If Paul was anti-Sabbath as "Christians" make him out to be, he would've insisted that his Gentile audience in Acts 13 hear him preach on Sunday instead of Sabbath.
As to Paul insisting on preaching on the first day of the week (what is now known as Sunday) see Acts 20:7.