What you say is true of course Jim. The colonists weren't there to help these countries to develop, but to plunder their resources for their own ends. Sadly, there are numerous Lebanese, Chinese and other 'investors' still hanging around in W Africa, getting very cheap labour and exploiting the native people. As a young man, my husband worked in incredibly difficult conditions with 50Kg (!!) sacks of cement on his back in 40 degrees of heat for £30 a month, for a foreign construction company. He very nearly died.
But the upside is that development did take place (probably to benefit the incomers, not the indigenous people!)
Dakar, Accra, Abidjan etc seemed to me to be great modern cities, and there have been some advantages. But abject poverty is still to be seen on the streets. Starving beggars and skinny children etc.
The interesting thing is that deep in the countryside, the people live as they have always done, and they seem content and in reasonable health. In Nafamadougou (husband's ancestral village) they have a dignity and pride in their un-modernised ways.
(But the last time he was there, an old bloke, the 'headman', asked him if he could buy them a tractor in UK and ship it out!)