Missouri was not one of the original 13.
Regardless of whether Missouri was one of the original 13 states, the Constitution makes all states equal. Also, the 14th amendment requires all state laws and constitutions to comply with federal standards for civil rights enumerated in the US Constitution. Even thought the US Constitution bill of rights only applied to how the federal government treats citizens, the 14th amendment applies those and subsequent standards to the states.
It’s not just the Fourteenth Amendment; it’s also the Supremacy Clause of Article VI Section II.