The reason why there are no competent Sudanese to run the country is specifically because colonizers went in and destroyed all of the home-grown institutions Sudan had and replaced them with ones locals didn't trust, but were more legible to the colonizers. This is why decolonization has been a failure in some countries: removing the boot doesn't help after you've smashed someone's face in.
The countries that did benefit from decolonization had a unique pattern to them: they all had lacking or inadequate institutions before they were colonized. But colonizers don't build infrastructure for free, and the people being colonized know that. Colonial infrastructure tends to only be good for the needs of the colonizers' resource extraction industries. That's what puts distrust into the heart of the people in those countries in the first place, and why the success stories are rare.
You are correct that some sort of political force needs to be put in place to serve as a functioning institution in Sudan. However, colonial powers are very bad at doing that, because it's easier and cheaper to just smash and grab.