Lifejackets are improving the safety but not that much as assumed.
Controlled ditching is a very rare case. You would not need a lifejacked after uncontrolled ditching.
OK, if you there is a ditching somewhere in Carribean, and you have managed to escape unhurt, and you are lucky to avoid sharks, lifejacket could save your live.
Many years ago I have passed SOLAS (Safery Of the Live On the Sea) training program, which is mandatory for all professional seamen, and can assure you that you will not survive in the Baltic or Nothern Sea (and all similar places) from October to April for more than a 5 to 30 minutes, doesnt matter if you are wearing the livejacket or not.
If someone really considers that livejackets are really improving the safety then they should start to press for mandatory ejection seats for the passengers... Ejections seats will double or triple the industry expenses (which will be passed on to the passengers) but they will save much more lives and will improve the pax safety even if every second pax will not survive after ejection...