I never claimed that colonisation was done for the benefit of the natives or something like that, but to reduce the colonial question to economical interests is again, vastly oversimplifying. British involvement in India is an extremely complex subject and while it was originally indeed done by a "commercial" company and for economic reasons, it then evolved in ways that went far beyond purely economic rationality. This is even more true about Black Africa which was never really profitable as a whole, exactly as you are stating. It was much more a question of prestige, and whatever economic benefits were at best the cherry on the top of the cake and most often nothing more than propaganda prospects. For all that matters, political decolonisation didn't always mean economic decolonisation. In French Africa, all of the French compagnies that were exploiting natural ressources stayed. They are still there today, 50 years after independence.
What I am trying to underline is that you underestimate the great variation in the policies the colonisers applied in their colonies, and those policies
were vastly different from one colonising power to another and even within the same colonial empire to be honest. This is not even a question of intent - you could very well have a lenient policy motivated by the conviction that it is the best way to control and exploit the population, or a disastrous policy fuelled by a genuine desire to civilize the natives. Both certainly existed. I challenge you to charge
this man with racism and contempt against the Blacks. Of course, most of the colonisers never actively cared about the natives' quality of life or about preparing them for independence. But as a result of the policies they applied, some countries ended up better prepared for independence than other. This is an obvious fact.
And the other very important aspect that you are ignoring completely is the role of the native elites, who generally overtook the power after independence. The relationship of these elites to the colonising power is very interesting and complex, and a large part of the question of "state-building" can be answered with that. As you have said, there were virtually no educated native elites in Congo for instance, but this was certainly not true in other places. Senegal and the Ivory Coast were overtaken by men who served as Cabinet ministers in the central French government before independence. So it was very interdependent and complex, and the picture is very different from one place to another.