This is pretty much how I felt when I read the DMG for the first time. I didn’t realize so much as the then, but it became quickly apparent that players that evolve into DMs have essentially become game designers. They fiddle, they change, they make up, delete, add to the rules and play of the game.
Designers who write books, should remember this feeling when they publish games. These are the things that happen at the table or behind the screen that sometimes are forgotten when sitting behind the desk.