The trouble with setting up systems of authoritarian government is --
You don't really set up systems of Authoritarian government; the whole point of authoritarianism is that your own opinions and desires are off the table. You either handed them to the violent jerk with all the guns because you were dumb enough to vote him into a position where he could swiftly murder all his opposition; or, in ye olden days, he murdered his opposition without ever having to stand for office in the first place.
Either way, you've got a system that is devised through killing, which means that when someone decides that they want to be the next autocrat, they have significant precedent on their side that supports bumping off the current autocrat.
Which is why, even though Kingships were stabilized by adherence to law, custom, and religion, they were not, in fact, very stable. Uneasy lies the head that wears the crown, and all that. Sometimes you had stright-up wars for dynastic succestion, such as the Thirty Year's War; sometimes you just had poison and backstabbing. Or frontstabbing, in the case of Caligula's demise.
20th-century dictatorships were like this except without being propped up by custom or religion, so all they had was the fear of violence without granting their subjects the emotional buy-in of tradition and God. The question of how well that worked depends upon how many such dictatorships remain. It seems as though we have a lot more parliamentary democracies across the world, now, or at least we have a lot more countries who have a facade of democracy while the real players do as they will. Even the autocrats understand that you have to have some kind of popular assembly, in order to replace custom and God as the people's emotional buy-in, so that the regime has some kind of stability from legitimacy.
I think that's one of the unspoken benefits of democracy, not mentioned often because it's fairly cynical -- the idea that voting creates a bond of identity between the people and the government. You punch your ticket for a candidate and if they win, they're Your Guy, dammit. This is part of why incumbent politicians tend to win.
In that sense, democracy allows for much greater stability of government than monarchy, even if in the short term swapping ministers out every few years looks chaotic.
Meanwhile monarchies tend to murder whole swathes of people who rise up in the inevitable peasant's revolt based on the latest heavy tax or miscarriage of justice or social inequality. Wikipedia's list of peasant revolts is long indeed, for monarchies have by necessity spilled much blood in maintaining the stability that modern monarchists say is natural to autocracies. (Saudi Arabia is currently engaged in such an effort to put their client state of Yemen in its place.)
Modern monarchists have no clue how much killing it takes to maintain an autocracy.
If they do, and they still want a monarchy, that's a good time to run.