I might argue with you take on DM authority. What is possible there really isn't what's the same as usual, or normal, or taken as the cost of doing business. DO you see the distinction I'm trying to make? I'm not talking about run of the mill call-making.
Once you start talking about the rules not having force you've dropped the ball. Of course the rules don't have force. What does have force is the social contract at the table, and that, my friend, normally doesn't include random and rampant rule changing.