Uhh...
Simplicity is why i enjoy it. Or did you think you were change my mind by saying akuma came out first or something.Akuma came first and was a cool easter egg in SFII. When a character first appears in a series like this, it makes a strong statement, and being around forever kind of gives him a pass regardless.
Simplicity has nothing to do with it. Oni is 'we're out of money AND ideas' the character.