Correct that it isn’t vague. It means “well functioning” as they would have used it. A contemporary would have said a clock that keeps time accurately is “well-regulated”. It doesn’t refer to bureaucratic regulation in the slightest, as you can compare how those topics were talked about in the same documents of the constitutional convention and the Federalist Papers etc. and the verbiage used is completely different.
People in those days used flowery language such as Washington’s quote “Let us raise a standard to which the wise and honest can repair.” He isn’t talking about wrenching a bicycle.
It also takes deliberate ignorance to read a list of 10 individual rights and construe that one in particular is somehow collectivized and handcuffed by a footnote about its justification.