The “well-regulated” phrase was interpreted by the Court in the context of being part of a (merely) introductory clause.
Same effect as excising. It means they intend to ignore it. Strict constructionism, just bring scissors.
But the phrase still has operative effect. That is why the Court held dangerous and unusual weapons can be banned because they aren’t the kinds of weapons that belong to a “militia” as conceived when the Constitution was drafted.
Neither were breech-loaders, but see how they draw the line wherever they wanted it to be in the first place?
The line is drawn at weaponry in common use. Given the definition given to “militia” by the Court it does flow logically.
The ruling creates it own contemporary “common use”. Machine guns (Tommy guns) were once pretty common. Now they’re illegal, and they’re not anymore. Ban breech loaders and eventually they won’t be common anymore either.