Reverse Incorporation?

Let's assume that the Second Amendment, when ratified, was understood not to convey an individual right. Let's further assume that in 1868, the Second Amendment was generally understood (incorrectly) to convey an individual right to keep and bear arms for self defense; and that the Fourteenth Amendment, when ratified, was generally understood to convey (among other things) this individual right against the states.

I assume that, in a suit involving a state, or a subdivision of a state, the 1868 understanding would control. But the case the Supremes have just accepted involves the District of Columbia. The District is not a state. The Second Amendment, but presumably not the Fourteenth, applies to it.

Which understanding then controls? Is the 1868 understanding somehow "reverse incorporated" back into the Second Amendment itself? My recollection is that Akhil Amar discusses this somewhere and would answer in the affirmative. (I believe the discussion was not about the Second Amendment in particular, but about whether 1868 understandings of provisions of the Bill of Rights, applied against the states via the Fourteenth Amendment, should in general be deemed to relate back to the underlying provisions of the Bill of Rights.) My recollection also is that I read and reread Professor Amar's discussion and could never understand it.