The "safety card and safety brief" have nothing to do with safety. Apart from the seat belt stuff which every car occupant understands, the rest is an emergency response procedure, which the cabin crew are supposed to be experts in.
That's right! Every car occupant understands how to operate the seat belt because they do it every single day. It is deep in their instinctive memory, They reach down the side of the seat and click the little red button. So in an emergency situation involving high stress and panic their short term memory will (if they watched the safety briefing) have been told how to operate the seat belt. Those that neglected to refresh that part of their survival toolkit will revert back to instinct and reach down the side of their seat to find the little red button....only guess what.... it isn't there! History has the names of plenty of corpses that failed to survive perfectly survivable events but were still secured in their seats. Many survivors have recounted tales of reaching instinctively for the seat belt release down the side of their seat.
Of course this is why as pilots we brief prior to every take off and landing. We are putting the important points of that brief back into short term memory and thereby beefing up the toolkit.
So when you say:
The briefing is a CAA (and other regimes) requirement which has nothing to do with safety. I am sure that the pax on MH370 were given a "safety briefing"
You are wrong! It has everything to do with safety. It may not guarantee your survival but it is designed to enhance your chances. Would you like a very long list of flight numbers where the safety briefing did contribute to a successful outcome?