Your thought and you measuring is not new ~ and I'm sorry, but although mathematically you are correct, physiologically and psychologically you are incorrect.
Without the 'necessary' amount of sleep, human lifespan would decrease ~ DRAMATICALLY ~ simply through the sheer number of road traffic casualties, airline crashes and surgeons and anaesthetists plain mistakes and basic screws ups.
Lack of sleep, for example, has caused nurses and doctors to administer both the wrong and FATAL doses of drugs. The results are experienced not just to the life of the deceased, but to their families etc.
If (by some chance) you truly believe in what you are suggesting, then I hope my life is never reliant on your ability to stay awake (as selfish of me as this might seem to be) and alert ....or that of anyone else either.