There's actually no "good" or "evil". Just two different ideals.
Hieron believes that one supreme power should rull over all (believing all the while that they're benevolent) to prevent uprisings and enforce the law, refusing the risk of despots coming to power and corrupting the empire. The flaw here is that it only works when it's ruled by a fair hand. The moment a greedy heir decides to take advantage... all bets are off.
Whereas Union believes that individual states should govern themselves,suffers the risk that other regions may bicker/war/dispute, but in any case they all get to choose how they live and can prevent an idealistic regime from imposing their ideals. The downside on this is that you're in a constant battle of diplomacy trying to keep everybody friendly.
So which is better? An empire that can provide security only for so long as the empire has the best interests of the populace at heart and is susceptible to corruption? Or city states that can actively work to observe and adjust treaties based on economic benefits, but suffers continous minor conflicts to keep it alive?