An autocratic country could easily spread propaganda in the democratic country, because of “free speech” rules that most democratic countries have, but a democratic country cannot easily spread its propaganda in the autocratic country.
An autocratic country can buy an election in the democratic country, but the democratic country cannot easily coup an autocratic country.
Are all democracies are doomed to fail?
Is the future of humanity, autocracy? For the rest of humanity’s existence?
I think your questions are more complicated than you realize.
If you separate the form of government from the governing, yes autocracy is a superior form of government. A dictator can instantly marshal resources to face any threat, or completely shift an entire nation, if a direction becomes clearly wrong. The reason they don’t work, is because the leader is always human. Humans make shit leaders, almost always. So distribution of power across a large number of people mitigates the risks of putting it all in one.
Yes. Obviously. Everything eventually fails. The Sun will fail and take the earth with it.
No. Obviously. Everything eventually fails. The Sun will fail and take the earth with it. I would hope humanity (or whatever species humanity evolves to) lives past that.