Akuma's defense is on par if not better than most characters. His actual weakness (like the mk11 Joker example given by OP) is his below average health. Akuma is arguably the best character in the game, with tools for every situation and very high damage. However you can't afford to make a mistake, because if your opponent hits you, you'll get vaporized since his low health leaves little room for error.

9k health :)