Why does it matter if the choice of taking levels in a class is for optimization/powergaming or narrative reasons?
I am pretty sure in the context of high fantasy a player can come up with a creative story for why their character is a paladin (devotion)/rogue (assassin)/cleric(knowledge)/warlock(chain/great old one) ohh and a half dark elf. Let's just assume this absurde combination is done for some cheezy exploit, what is wrong with that? Make the fluff work.
I am pretty sure in the context of high fantasy a player can come up with a creative story for why their character is a paladin (devotion)/rogue (assassin)/cleric(knowledge)/warlock(chain/great old one) ohh and a half dark elf. Let's just assume this absurde combination is done for some cheezy exploit, what is wrong with that? Make the fluff work.