No, judges are not kings. The concept of a judicial branch came as a response to monarchies in which kings and ministers were given unchecked executive and judicial powers. That doesn't mean the judicial branch can operate without having laws and standards to prevent proceedings from falling into chaos. Shkreli and lawyer were made well aware of these laws.

Are people computers? It's not always perfect, but judges ideally have leeway in sentencing because the circumstances around the same crime are always different. A person that actually understands the gravity of a crime and is remorseful shouldn't get the same sentence as someone who has no respect for the law and seems willing to repeat the same crime or similar. It's actually a pretty big complaint about mandatory minimum sentencing when it is used against poor people of color.