“The right to keep and bear arms is among the privileges or immunities of United States citizenship...”

I think that’s wrong. The Constitution does not create the right to keep and bear arms. The right itself is neither a privilege nor immunity created by the Constitution.

However, the Constitution does explicitly prevent the federal government from infringing that right. The people’s freedom from molestation of that right IS a privilege of citizenship...one that should be applied to the states.

In modern times privileges and immunities language is often associated with being allowed to do things by the government. My research indicates that in earlier days privileges and immunities were simply alternative terms referring to rights - all of them.