It’s not an assumption, but a conclusion based on the evidence. I’m not aware of any Asian, African, or middle eastern country where freedom and democracy led to prosperity. There’s lots of democracies in these places that haven’t been able to translate that into prosperity. On the flip side, China, Japan, Korea, and Singapore are all examples where authoritarian rule has led to prosperity. I’d include Bangladesh these days as an example of that also.

If the country you’re using as an example is in Eastern Europe, I think you may be overlooking key differences. Fareed Zakaria addresses this in his book “the Future of Freedom.” https://www.amazon.com/Future-Freedom-Illiberal-Democracy-Re.... He explains that many of the foundations of liberal democracy were put in place during autocratic regimes: https://en.wikipedia.org/wiki/The_Future_of_Freedom. Eastern Europe had many building blocks of democracy in place hundreds of years ago. For example https://en.wikipedia.org/wiki/Cossacks.

Hong Kong had what one could call a starting position comparable to Singapore after WWII and managed to become prosperous with arguably more liberal policies -- until the handover to the PRC -- and came out prosperous, too.

Is Hong Kong now more prosperous, after it moved to authoritarian rule?

What are your criteria for "authoritarian", that you count Japan among authoritarian countries?

What is your evidence that the authoritarian policies were the deciding factor in generating prosperity for these countries?

Hong Kong was a colony where all significant decisions were made by a European power. (Which imposed economic, legal, and political systems that it developed during a monarchy.)

Yeah people had personal freedom, but they couldn’t do anything with it.

Authoritarianism led Japan into a war which utterly destroyed its economy. I'm not sure you can count that as a win for the jackboot.

The barriers to development is not how much wealth the society has currently, but the the absence of the underlying social and economic infrastructure that makes growth possible. Germany was ability to rebound from two wars that destroyed its economy while numerous other countries languish.

botswana is an example of a country where the first/strong leader built democratic institutions that kept the country safe and growing. Obvious to cite diamonds resources, indigeonus leadership, societial values like private property but those dont diminish its miracle. democracy or people participation can look different in differents countires for sure, but PAP undermine any competition in shady ways

Where are you from?