It doesn't matter if colonialism caused *any* problems or not. What matters is that colonialism doesn't doom a nation to perpetual disaster even after a nation has freed itself from said colonialism.Singapore, Hong Kong, and the U.S. easily show that former colonies can rid themselves of their colonial masters and then go on to thrive under their own management.
This is important. If people erroneously believe that they are doomed *because* of colonialism, then they may give up the intellectual challenge of trying to figure out how to solve their own problems.
"Oh, we're victims of colonialism, so we can't solve our own problems" isn't going to save Africa. They've got to rise above it, and they've got to do it on their own.
Blaming colonialism won't save them. Outside aid won't save them. New African leadership won't save them.
The *people* themselves have to want to make their nations better.