If you list thing like running water, electricity, cars etc as the benefits of colonialism, you are indirectly saying that black people would not have been able to implement that in Africa themselves. And that is racist, whether you like it or not.
China never colonised Brittain, yet the Brittish have gunpowder.
The Arabs never colonised Germany, yet the Germans have Algebra.
The US never colonised Russia, yet the Russians have light bulbs.
There's nothing to indicate that Africans would not have been able to incorporate "western" technologies into their infrastructure if they had not been colonised.
If you want to extol the legacy of Colonialism, you should focus on things that would be almost impossible without it.
you ignoring the reality of the people here still in hunter gatherer phase. nothing had happened here for thousands of years, it would not have happened all of a sudden. the rest of the world was using gun powder and horse and carriage and ships, had businesses and government and individualism. these things were all available and there during that time, but southern africa was not using it. why would it change all of a sudden.
those other countries you try and compare southern africa to were far developed themselves, nothing like that existed here. china was ruled by britian for over 150 years too btw.
the historic empires colonised where ever they went. they applied their technology where ever they went.
if the ships simply sailed past the southern african coast line, the tribes would still be living in huts with leather loincloth clothing today. some people still do. pointing to northern africa as a counter argument is futile since they were ruled by another empire too
and just because one group of people moved over land and could not fathom the idea of moving across the water, does not make them better than the people that crossed water. both plundered and pillaged. the one was just far less advanced than the other, therefor weaker and overrun.
how many years do you think it is reasonable for a hunter gatherer society to truly embrace and catch up to a modern one. keep in mind there are forces working against this, culture, habits, beliefs, superstition, xenophobia, racism.