Woah, nobody was talking about race here, why are you suddenly bringing it up?
Oh, interesting, because you're treating time and ethnicity, as the only factors in economic development. If you take a country full of Ugandans, and a country full of Singaporeans (the countries in your theory are the same of course), and terminate "colonization" (which is the same thing everywhere) at roughly the same time, if the Singaporeans do better, that means the Ugandans are... stupider? Less good at capitalism? What's your full, stated theory here? Can you please say it outright?
Anyway, you're ignoring a lot of other relevant factors. The two countries decolonized at roughly the same time, however Singapore is a tiny maritime city-state, whereas Uganda is a large, landlocked, agrarian country, and its agrarian economy completely taken over by cash crops.
Btw it's also a bit bizarre that you're just saying, "Africans." Africa is a huge continent with wildly different ecologies and economies across it. Regardless, Ugandans do indeed have agency, and that agency is the same as anyone's agency: operating within the constraints into which they were born.