> setting up the president as the sole power center is an inherently unstable system
Only if there is a transition of power. If power stays in the same hands, the system can be very stable - and not in a good way.
Trump is pretty old at this point. Even if he decided to go full dictator, how long does he have? Maybe 5 to 10 years? I don't think it would be quite as "stable" as Putin's Russia.
> If power stays in the same hands, the system can be very stable - and not in a good way.
I don't think it actually can be that stable. I think I see what people are getting at when they say this, but it seems to me that authoritarian governments are generally quite unstable, because power never stays in the same hands. Power always changes hands, because we are mortal. Non-authoritarian systems are built to handle this, and ensure that it happens frequently enough that the wheels stay greased. Authoritarian systems are built around ensuring that the concentrated power stays only in the hands of certain people, and this is not possible.
To put it another way, non-authoritarian governments have less variance because they are taking some (very) rough average of all the people. Authoritarian governments are much more subject to the significant variance of individuals.
Of course we don't actually have that much historical data on non-authoritarian governments.