Well-regulated in that context means “well-trained or well-maintained” not controlled by government.
Yes, well-regulated in the context means WELL TRAINED. Not that their actual firearms were regulated.
If that were the case we’d have seen a reference to this in their Federalist Papers or someone’s recorded speeches. IT IS NEVER MENTIONED in the context of determining acceptable firearm characteristics, it is ALWAYS mention in terms of a trained and able militia in case they need to assemble and deal with a threat.
“well-regulated” in 18th century parlance meant something that worked as it should. Such as a “well regulated time piece”.