Given that we have exactly two instances of countries that had a billion people, you're cherry-picking (whether or not deliberately).
You could argue that more countries have rapidly emerged from poverty while controlled by a dictatorship than controlled by a democracy. (Even South Korea would qualify for that.) But your "a billion people" threshold makes it look like you want to shut down debate, rather than actually look at data.
> you "a billion people" threshold makes it look like you want to shut down debate, rather than actually look at data.
Not so - the threshold is there for a reason. It's inherently harder to corral more people than fewer people. At the time that South Korea became a fully fledged democracy, their population was between 37 and 45 million people. That's roughly the size of the urban area of China's 3rd largest city.
You cannot control a country of 1.3 billion people (with a landmass larger than the continental USA) that has regional cultural differences such as diet and language as easily as you can a homogeneous population of ~40 million in an area the size of Indiana.
If I wanted to increase the GDP of the city block I live on, it's a lot easier than if I wanted to increase the GDP of my entire city, let alone the county, state, or country. Things are harder at scale. That's where the efficiency of a dictatorship shines. Not that I'm a fan of The Party, or of dictatorships. Fuck them both. I've done business with The Party, and 10/10 would not recommend. But credit is due where credit is due, and The Party has managed to do some things that have been incredibly beneficial to China at large, on multiple fronts - economics, infrastructure, education, etc... Part of their ability to do so comes from having a centralized dictatorship.