Well if it's exaggerated, do you have a more accurate map? How did colonization suddenly make the terrain easier for state building?
Colonies were just pieces of land assigned to European countries, but the method of colonization was by extraction, hence the building of settler economies. There were certain areas that never even saw Europeans because the terrain and climate were too harsh for them to survive and these areas in these ex colonies claim marginalization till this day since they did not get the good nor the bad of colonization, and there is usually free movement of people from these areas from one country to another especially among pastoralist groups.
Regarding the map, Take Uganda for instance, which falls under total Bunyoro-kitara occupation, whereas in the region at that time period, there was the expanding Baganda empire,The Toro and Busonga kingdom, the Acholi and Lango pastoralists, The Teso who had their own leader, etc. Making a map of Africa based on former kingdoms is as impossible as making a map of the middle east in 2000BC when empires were rising, falling and borders constantly changing due to the multiple ethnic groups living there at that time, and Africa was like that, times 1000.