Just because it's fantasy doesn't mean there should be no logic, but that's not the point. When politics isn't the focus of a work the only reason to bring up something like Democracy is to have an easy Good (democracy) vs Evil (monarchy). It's boring
If you value civil rights, then yeah, Democracy is pretty much always Good. Though still a frustratingly imperfect system in an imperfect world, but they're definitely a better place to live than dictatorships. CGP's Rules for Rulers covers all this nicely.
Sp yeah I don't mind fantasy authors using Democracy as a shorthand for "Good". Because "Good" usually does entail more freedom and happiness, whereas bad guys in fantasy stories usually want to rule with an iron fist.
Mind you, I don't mind if you find it frustrating how it's treated as an easy transition. Because that's really not how things are at all. But if you're reading slop like this manga, I'd assume you sometimes enjoy slop. I know I do.