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?
Quite the opposite. Due to systemic corruption autocracies are economically highly inefficient with low productivity across the board with all kinds of long term effects this brings. And while it might look bad for democracies at the moment, I think many of the current crop of autocracies will be short lived. In the end, economy is where it’s at, and autocracies are horrible at it.
It’s one of those things where evil people actually don’t win - it just looks like it on the short term!