Well in that case I fear it might not be the DK's being very strong, but more the case of your characters are weak.
Madora should have a pretty decent amount of gear by now and assuming you saw the insane potential of glass cannon, she should have that aswell. That should lead to Madora being able to instakill them with a flurry. Oath of desecration+rage+flurry = (death)knight *pun intended*
There is even room to cast nullify resistance and assuming madora goes last from your 4 characters you can have somebody else cast the oath of desecration or wildfire for that matter. Blinding/stunning them or freezing them are also valid options after you have lowered their saving throws with drain willpower/divine light etc. etc.
If you do have an archer related character which hopefully also has glass cannon you should be able to cc 1-2 before they even get a turn via stun arrows/knockdown. Which should all synergize with bully.
With kind regards,
Rashar.
