One must take into perspective the nature of D&D Paladins and how White Wolf depicted them(by following the 2nd Edition). D&D Paladins in the 2nd edition had Undeath Immunity, Disease Immunity, Smite Evil and Detect Evil.
Clerics are Melee Capable in D&D terms and can wear Plate like Paladins so an Evil Paladin of WoW(like the Scarlet Crusaders and the Lightbound) would just be a Cleric of the Light and not have Detect Evil or Smite Evil due to being a Fallen Paladin.
Clerics of Light have access to Light aligned Spells including Searing Smite as well as Flame Strike… Yes the Clerics of Light have Fire Abilities in D&D that deal Radiant Damage unlike their counterparts from the Clerics of Fire…
Clerics aren’t immune to Disease or Undeath despite having Turn Undead, Searing Smite and Know Alignment…
In otherwords Crusader Bridenbrad whom the Naaru just took to Paradise due to being inflicted with the Undead Plague is a Fallen Paladin and thus merely a Cleric of Light by D&D standards!