
Lets just say whitebeard wanted to make ace the next pirate king
is he retarded ?
Ace didn't carry the will of Joy Boy or Nika and that's a key reason why the Gomu Gomu no Mi chose Luffy from the beginning. Remember, every Devil Fruit has a will of its own and ultimately chooses its user. Luffy's fruit chose him over anyone else.
So the real question is that did Whitebeard know what it truly takes to be the chosen Pirate King?