It isnt vague
It clearly refers to a well regulated militia.
I suppose they could have put the initial clause in bold/highlights/underline and all caps. Though Idont think it would help. People read what they want to read.
Maybe changing “The people” to “those people” ?
A WELL REGULATED MILITIA being necessary to the security of a free State, the right of those people to keep and bear Arms, shall not be infringed.