It's a fair complaint. WAR has always been the dungeon tank because of the broken sustain on it, while DRK has always been more of a raiding tank due to having more mitigations and more damage, but even beyond that... DRK straight up has to work harder.

The button input for DRK is way more than the input for WAR is, and that alone to me should be enough of a reason to see DRK have better damage. More effort being put in should result in more results naturally.