You've hit the nail on the head of one of the biggest problems Eskom is facing at a ground level that is increasingly difficult to fix.
In any engineering sector, the process of individual growth and skills transfer is simple. You have the experienced senior engineers with all the institutional knowledge, practices and skills. They work with upcoming engineers to transfer that knowledge so that when they retire or move on, the next generation steps in and does the same, rinse repeat.
Eskom bypassed this process with the transformation wave and retrenchments it did. The senior engineers were forced out, immediately pushing the next generation into their position. Those people are now holding senior titles, but they weren't ready and have lost out on years of mentorship and handover that was supposed to happen. Those that are actually senior are spread far too thin.
How do you recover institutional knowledge once it has left? Well, you can't really, you have to rebuild it from scratch or bring the people back in. Depending on the complexity of the projects (and Eskom is extremely complex), you could never recover from such a blow, perpetually stuck in a death spiral.
This is exactly why companies fight fiercely to hold onto their senior engineers, it is an incredibly costly and lengthy process to fully replace them. Lose enough and you no longer have a functioning company.