Justinian I,
Stop pretending to be a dolt.
Autocrats choose their heirs. Augustus chose Tiberius. Tiberius chose Caligula. Your example, in only 2 generations, directly led to Caligula.
Democratically elected officials are chosen by the people. The people led to Jefferson. The people led to FDR. Did Jefferson choose heirs who messed up and chose Obama? No. There's no parallel. That's just stupid.
"4. The best you can say is that democracy takes longer to become illiberal."
How illiberal a government they elect depends on the people and their education and values. At any time, they can, through education and values, elect better leaders. This is a mechanism to keep government liberal (if that's their choice) absent in autocratic government.
Want more liberal government under democratic government? Convince people to agree with you and you can make it happen. Want more liberal government under autocratic rule? Keep it down or you might be imprisoned or put to death.
This is a huge difference which makes democratic government structurally more liberal than autocratic government.
Duh.
Because of the corruptibility of man, many have argued that government is inherently illiberal for centuries. I tend to agree with them. But some are more illiberal than others. And autocratic government is inherently far more illiberal than democratic government.
Decades means nothing. Good job, autocracy got lucky with a ruler for a few years. And that ruler was followed by illiberal garbage, as they always are. Score 0 for autocracy not being inherently illiberal.
"You are highlighting how an illiberal successor is more likely to result from an autocracy that practices hereditary succession."
Your examples are of peoples who adopted and had great choice in their successors. They weren't entirely trapped. And your implication that virtuous people could ever appoint worthy and liberal successors for any sustained period of time is laughable.
[I wish I could obey forum rules]