"Second, in my opinion there is absolutely no justification for torqueing a breech plug that tight."
When fitting a plug instead of fitting the plug perfectly, you can skip the last half dozen adjustments and just mash it into index by brute force. That saves time. It also dissuades end users from messing with the plug.
The guy who buys the barrel probably will not have a professional quality vice, blocks and wrench. So he is at a loss on how to get the plug out. If you fit your own plugs then a bench vice is fine. You can control the torque required to make it index.
There is a good chance that a bench vice will not work to remove the factory fitted plug. I wince when I hear about guys trying to use leather or lead to protect the battel form the vice jaws. That is a recipe for disaster. You probably will need a real barrel vice and real fitted blocks. You won't know what you need until the plug unscrews or the barrel is buggared. Wrenches matter too, it does not fit perfectly, and is stout, and you might ruin the plug. How many times have we all seen pipe wrench marks on old guns? Seems like this is a very old issue.
Leaning on the cheater bar and giving it a couple of wacks with a big hammer is a standard method to bust a barrel, or a ML plugs, free. Don't do this unless you have a top quality vice, blocks and wrench though.