I think there's a narrative similarity between Tarquin and Redcloak.

The story of Redcloak reminds us that many fantasy classics are based on a sentiment we would normally call "racism", or worse. Killing insert-enemy-of-the-narrative-here because of their species - is an action that, in real life, most people would deplore, and yet in fantasy literature we generally cheer for it.

Tarquin has an analogous role, for showing up another of the flaws in common fantasy classics. Evil empires constantly fall, but without regard for political realities. Some empires are not all that evil (cue "what have the Romans ever done for us?" sketch), particularly when compared with what came before or after them. And the plucky rebels, in destroying them, seldom take the time to put an alternative government in place to keep order during the "transitional period" (read: bloody anarchy) that invariably follows.

Just as Redcloak makes us think more about the first of these tropes (Redcloak is an evil goblin, and he needs to be defeated, but if we oppose him because he's an evil goblin we're doing something badly wrong), so Tarquin challenges us on the second (Tarquin is an evil emperor, he needs to be defeated, but if we just defeat him and leave it at that, we'll be doing something else badly wrong).