I stand by the answer given in #msg-68053216 that drug B is the better choice.
Conceding up front that the key to emphasis is repetition, and admiring your steadfastness as a general virtue, I still think your math makes no sense.
Everyone takes the 100% cure drug. Everyone. Not just 80% take it, everyone takes it. AND, it cures everyone who takes it -- iwfal did not say it cures 80% of the people who take it. He said it cures them all.
If iwfal had said, Drug A cures 80% of the people and then 20% die from side effects, AND we knew up front which 80% were going to die from the disease (which we don't), then your point would be valid.
I repeat, to create emphasis, that he did NOT say that: