RDD is a class limited in what it can do. It requires 2 class slots of 3, itself and another being bard or sorcerer. Likewise a third class is difficult due to the fact if you wish to do a PrC with a BAB requirement, you must go 5 bard into RDD and your BAB is brought to terribly low values.
Thus I would suggest that for the sake of build diversity for RDD, either the qualifying classes be expanded similar to that of Arcane Archer (Arcane charisma based classes such as hexblade and warlock as prerequisites) OR/AND the 8 lore requirement be brought to 6 from 8. The latter would mean one could go 3 bard into RDD till they qualify for classes with a higher BAB requirement without ruining their BAB or level spread such that the third class is defeated and gains little to nothing.
Only note of concern could be potential for 16 BG, where 16 paladin has t2 oath 16 BG would net epic fiend. This is a consideration for balance I say for the sake of posterity.