What support do you have for this assertion? The Church is legitimate heir to the Old Testament through Jesus Christ and His Apostles. Rome added nothing that was not already among the Jewish canons. The Masoretic Text did not exist in its final form until many centuries after Christ.
Rabbinic Judaism recognizes the twenty-four books of the Masoretic Text
Again, the Masoretic Text does not contain the books of Ecclesiastes, Song of Solomon, and Esther. These books are, however, included in the Protestant canon. Do you disown the Protestant canon?
Again, the 'Masoretic text' DOES include the books of Ecclesiastes (Kohelet), Song of Solomon (Shir HaShirim), and Esther.
If true, this would mean, according to the (non-Septuagint) OT canon and Zakkai's school, Jamnia c.90 A.D. :
Jesus is *not* the Messiah, there is no afterlife reference in the OT, and there's a curse on converts to Christianity.