From my understanding that is partially correct, the second amendment has never been "incorporated" via a supreme court ruling on the 14th amendment / due process clause as the others have. While logically it WOULD be, it has not yet been so I would imagine that leaves the states free to regulate arms however they see fit, and many state constitutions do not even mention the right to keep and bear arms (fun game: guess which ones)
That is my understanding of the situation at least, if a forum lawyer is out there to correct me, please do.
That is the currrent legal fiction. It has no bearing on how the Founders wrote the Constitution.
Please show me where in the Constitution this "incorporation" theory comes from. Might also be a good idea to read Article VI.
The courts have created a legal fiction of "selective incorporation", notwitstanding the fact that the original intent of the 14th Amendment clearly requires a full incorporation of Amendments I-VIII (the Ninth and Tenth don't contain any specific guarantees to incorporate).