“Well regulated” in the context of the constitution clearly meant well-trained/mobilized/deployed, in an efficient and orderly manner, and should be adequately capable. This is clear if you look at it from an unbiased linguistic standpoint, and look at the usage of the phrase around the time. Words don’t constantly have the same exact meaning that we’re primarily used to, they’re a spectrum of different definitions that form, morph, and wane over time.
Plus the first/second clause in the sentence is clearly just a justification for the other 2 clauses, it’s not a directive or even the subject. That alone would make the “well regulated” part meaningless for anything other than explaining why the constitution is in place in the first place. It doesn’t give orders to “regulate” militias, or even that militias are the only things which should have access to guns in the first place.
The point of arguing against current treatment of guns isn’t to argue what the syntax or basic meaning of the amendment was, no that’s clear if you actually know what you’re talking about (and you can find plenty of actual linguists breaking it down for you), it’s to argue to what extent the amendment’s directive (disallowing infringement on the people’s right to bear arms) applies, or especially if the amendment is even beneficial or if it’s harmful to a modern America and should be amended.