Just a short remark:
2nd Edition never claimed that he was an overdeity. That was the result of hyped fanon ignoring what the very book that introduced the base concept on which said fanon was build stated without any doubt: He was a greater deity (Guide to Hell, page 48).
Asmodeus (2nd Edition AD&D)
Asmodeus was never detailed in 2nd Edition and in fact was never even named until about a dozen years after the release of 2nd Edition because of the idiocy of the Angry Mothers From Heck and their ill-conceived crusade against the game. When Asmodeus did finally get a mention it was to suggest that he was a fallen angel overgod whose true form was a great serpent/dragon whose fall created the Nine Hells. The humanoid form was just some sort of Avatar or Aspect of this true being.
2nd Edition never claimed that he was an overdeity. That was the result of hyped fanon ignoring what the very book that introduced the base concept on which said fanon was build stated without any doubt: He was a greater deity (Guide to Hell, page 48).