Yes, people are 'just bad', that's why you don't design class mechanics solely around players who are already 'good.' You have to create a baseline where the average and below average can still participate that also allows for the gifted to excel. Dark Knights are a hook intended to increase the popularity of tanking and to help clear up the clogs in duty finder. The majority of them have never tanked before and aren't very good at it. They can't be left in a state where it's more difficult for them to improve their performance.
