Note since Charisma is at best a secondary attribute for the fighter or even worse if you want it to be at all effective it is likely Charisma + 2 or 3 even that and/or a proficiency bonus (not sure) especially since you made it a roll for every every taunting - they smashed it together in 4e both to simplify and avoid problems like .1/2chance x 1/2 chance to taunt = 1/4, or even 2/3 chance to hit x 2/3 chance to taunt... is 4/9
I assume most Knights/Warlords will make either Strength or Dexterity primary, then make either Intelligence or Charisma secondary. Depending on build. However, I assume a ‘lazylord’ Knight will make either Intelligence or Charisma primary, then the remaining Intelligence or Charisma secondary.
My approach is to make any of these scores viable depending on build: Intelligence, Charisma, Dexterity, or Strength. The Knight/Warlord would be Multi-Ability-Dependent to try cover all four, but I hope any two would work well.