The appeal to the text and original meaning of the Constitution is not about giving deference to 18th century attitudes over 21st century ones, it’s about resolving a dispute amongst two contemporary views. If everyone agreed that the framers were out to lunch on the 2A, it would be trivial to change it. But people don’t agree that the 2A is obsolete.
If you saw the word “arms” in a contract, would you think it was limited to a particular type of gun. If someone sells just automatic weapons, are they not an “arms dealer?” Like in a contract, if both sides agreed to change the word “arms” to something narrower, they could do it. But just like a contract, where the sides don’t agree, one is entitled to have the contract enforced as written.