Copyright exemptions (fair use/fair dealing etc) are a million times more complex than that. There are times when one adds almost nothing yet will still get protection. Take political humor. A standard bit is just to point out something funny. Look at how often political comics (John oliver/stewart etc) just play a clip of some politician. No edits. No commentary. The clip speaks for itself. That is still protected speech. Understanding how the comic adds to the clip cannot be expressed in numbers.