Not all Roman Emperors were ex-generals. For a time after Julius Caesar, the Emperor was chosen by birthright or appointed by the previous Emperor. This is how they got nutcases like Caligula and Nero as Emperors. (Historians debate whether Caligula was just that crazy because he was crazy or because he was mocking the idea of giving one man so much power, and whether Nero really was the incompetent despot history paints him as... but I digress.) It was only after the Empire began to decline that most Emperors became as such through military might and coups.
Whether he takes pleasure in it or not is irrelevant. He is a ruthless despot who is willing to use his own son as a (seemingly unwitting) lab rat and (apparently) not care that he died due to being an unworthy successor. That should tell you a lot about Varis' character.
If you repeat an argument enough times, it might become the truth! /sarcasm