The Constitution _does_ get to define what constitutes a “well-regulated militia”. Those who wrote the 2ndA soon thereafter wrote the Militia Act of 1792, so presumably it reflects what they had in mind. Of late, that was replaced with a new definition that defines able-bodied males 18-45 as part thereof, and implemented it via the Selective Service System to register members thereof and the DCM/CMP to train & equip them at their time & expense. Legalise often meaning something other than common vernacular, the term “unorganized militia” is nonetheless legally a part of the militia, and is demonstrably “regulated” to whatever degree Congress deems “well”.
RP, neither the 2ndA, Constitution, nor supporting law require that the “militia” in question be _owned_ by a state; the state may enact officers and provide some support & direction, but from the Constitution’s point of view there is only one “militia” addressed, not diverse “state militias” which you keep insisting decide who gets to exercise a “right”.
Make that "The Congress _does_ get to define".