The second amendment does not cover "how" arms can be kept.
The First Amendment does not explicitly cover "how" the freedom of speech can be exercised. But if someone wishes to write a book, can the government tell him that he must make a speech instead? Under your theory, the government would not be regulating the right to freedom of speech itself, but only "how" that right is exercised.
But I doubt that any court of law would agree that the government can force someone to make a speech instead of writing a book. Why? Because when the Constitution states that an individual possesses a substantive right, it implies the individual possesses the authority to determine how that right shall be exercised. The First Amendment guarantees not only the right to freedom of speech, but also the right to determine the manner in which speech shall be made; likewise, the Second Amendment guarantees not only the right to bear arms, but also the right to determine the manner in which arms shall be borne.
To quote from the decision of the Kentucky Court of Appeals in
Bliss v. Commonwealth:
"[T]o be in conflict with the constitution, it is not essential that the act should contain a prohibition against bearing arms in every possible form--it is the
right to bear arms ... that is secured ... and whatever restrains the full and complete exercise of that right, though not an entire destruction of it, is forbidden."