When those kings were deposed, rather than abolishing the structures those kings had created, they were instead largely preserved and put under "democratic" control.
It could be that this was a mistake: that there's something structurally intrinsic to the instruments of monarchies that can not be eradicated, regardless of who nominally controls them. ACAB.
In a democratic society with a Kafkaesque prison system, torture of prisoners is not as easily associated with any one person's cruelty. Because most people are optimistic and don't like to believe that several hundred million of their neighbors would silently condone the torture of a whole class of people, it's easy for lazy minds to consider prisoner torture acceptable, necessary, justified, and so on to whatever stronger beliefs these individuals may hold.
I'm not saying that prisoners would fare any better in a non-democratic society, but how people think of prisoner mistreatment would definitely be different.
Hypothetically, we believe in justice and freedom (and other good things and not bad things), or we would not have formed a democracy. Since we freedom-loving, democratic people would naturally act to end all oppression, it follows that if a policy, law or practice does not change then it must not truly oppress people.
Fiat-money Central Banks mostly were created under democracies, and seem quite resistant to change. Social-welfare programs. Anything related to lobbying.
I think the razor points to "institutions are highly resistant to change", not anything specific to monarchy vs. democracy.
(Not meaning to put words in anyone's mouth — just offering the thought the way my brain processed it.)
That does leave the question of what to do with those who commit the most serious crimes like rape and murder, but those are a small minority of the crimes currently prosecuted and are generally not the ones that best exemplify the failure of the existing justice system.
How do you enforce laws without enforcers?