christep, to obtain my F/A licence I had to pass various exams (here in Europe some countries have a Civil Aviation exam for F/As, like France and Italy to name two, and btw swimming skills are a requirement). One of those included extracting an unconscious BIG pax from his seat and dragging him in the aisle. We are taught techniques for doing that and exercise regularly (even too much if you want my advice
).
Regarding the swimming skills, I believe it is superficial to say it is no use. There have been accidents, like the Minerva one in Genoa, where one pax with swimming skills saved the lives of the other pax by swimming to the emergency exits and opening them. In this case it couldn't be the F/A who was dead. But next time the F/A could be the only one to be able to swim, to know where to go and what to do.