Finn, though grown, is a boy in a man’s body. While strong physically, unlike his Father Constantine the VII, Finn is mentally weak, self-centered, selfish, and resents his father for not making life easier on him. His father went through the military academy and served in the military early on and in the civilian sector to become well rounded and become a good leader.
While Constantine the VII did not find all the training pleasant, the experience made him the strong leader he is and he was thankful to his father Emperor Constantine the VI for forcing his training. Finn, going through this same program, has learned nothing. His pride and arrogance only fostered more resentment and hatred towards his father due to Finn's rebellious nature.
Finn cannot wait till his father dies so he can then hold the crown and have all in the empire for his bidding.