The plain point of the Militia Act of 1792 - if you follow its full wording - is to ensure the general population is armed, from which a subset thereof may be assembled into a unit. It made sure that any who could be called would be ready. It also established a minimum level of preparedness, not a maximum. It also assumed one would arm himself, THEN register as being so armed.
The first principle of the 2nd Amendment is that ALL may be armed, from which subsets may be extracted/called for active service. The notion that only those subject to active service be armed is plainly preposterous, limiting national defense for no justifiable (or even articulable) reason.
In a modern context, the aim of the Founders was to create an institution somewhat like the Swiss Army of today. I say somewhat because the level of training envisioned for the Militia (at least if you can call Hamilton authoritative) would be somewhat less than the Swiss system. On the other hand, the idea that (basically) all male citizens would own a military pattern rifle, ammo, and gear is certainly part of the original intent.
Then why does the Militia Act of 1792 say you have six months to arm yourself after being notified? Seems to me that if the plain point of the Militia Act of 1792 was to ensure the general population is armed, there'd be no need to allow six months -- the population would already be armed.