The reason that Africa is in a poor state of affairs is because of rampant colonization and pillaging by European settlers, of which enslavement was a byproduct. In your alternate universe where slavery never happened, Ethiopia and Mali would be wealthy empires.
If you wanted a better example, you might have picked, say, Benin. That you use Mali as an example of an empire screwed by Europeans in Africa suggests to me a general poverty of knowledge about any pre-colonial African history.
I am also not trying to excuse past behaviors or anything of the sorts. It was what it was and we always strive to do better when we know better. But that being said, systems are built around what is functional considering everything that can happen. When you account for everything to insure your safety and survival, it seems to work out like it did. On all sides.
And again, these interactions are never one way, longer term there's benefits to both sides, the local country, and descendants of all slaves and slave owners.
And just as an aside, I could very well argue most of us are still slaves today, but with clearly way better conditions and freedom of movement. But if you don't toil away daily, 5 days a week, you risk medical issues or lack of shelter, kind of like the homeless discussion in this thread. In some cases even death.
So putting what a few rich people from hundreds of years ago did, on me, a regular European folk, is shortsighted or even evil. I had nothing to do with any of it, my ancestors were peasants. And the same is valid for most people OP is referring to when saying "europeans". It's pure nonsense.