to believe that, you have to deliberately ignore many passages that flat out contradict your belief.
Nope. But they don't include it, either. In fact, the only thing in writing of that nature in the DMG is the optional rule involving plot points. Including it as an optional rule strongly implies that it isn't involved in the quotes that give the DM total authority.
Pretty much, yes. That's pretty much what those quotes say due to the absence of any limits. However, there are other quotes that say that the goal is player enjoyment, so if you're going to ignore the rules, it should be with fun in mind.