You Sir have it right. That is exactly what “well regulated” meant in the late 18th Century.
well-regulated == well-trained
He is correct. Another factoid that is ignored is that the Militia Acts came after the 2nd Amendment - likely to take advantage of the fact that the populace was guaranteed the right to be armed.
If they want to rewrite it, I would suggest, "The ability of a populace to defend itself from an overbearing government being integral to the preservation of Freedom, anyone who attempts to disarm the population will be shot".