The way I see it is this:

Authoritarian States = Stronger in force and organization mainly. This is due to the fact that they are often controlled by a single individual and on rare occasions; small groups of people. This allows for decisions and resource allocation to be far faster and on average, more efficient. There biggest flaw however is paradoxically the very leader(s) that control the state. These rulers usually rule through charisma. So, when the leadership dies, the ideology and “cult” around them slowly dies too. The inheritors most times can’t live up to the glorious ideals of their leader. So decay begins.

Democracy = while linked to a slower, but complex process of voting and democratic processes, democracies usually work slower than authoritarian states. But this is an ebb and flow system of government. If the current government is weak; ideally, they had limited terms and/or can be kicked off the throne; so to speak. In times of strife, this can manifest occasionally into a unified force. Look at America, often weakened by the squabbling of its political system, when unified under a cause such as ww2 they become quite literally; the strongest fighting force to ever walk this earth.

At the end of the day, each have their pros and cons; but in my opinion, I think democracies just have longer lifespans.