I think it's all a bit unrealistic to expect much else frankly. From my one experience of trauma I know that your brain does funny things and after a good shaking about you may well not know you are sitting down, let alone in an aircraft, let alone in an accident. I have read that some people struggle to undo their safety buckle and I can well believe it. The odds of me remembering how to open a door (and believe me I do try and remember it) - in the rather unlikely event I got to it first, are approximately zero. In those circumstances I wonder even if I had the card in front of me whether I could open the thing and deploy the slide.
That is why deep training is necessary so that muscle memory takes over, nothing casual will work. Passengers aren't trained and a two minute speech on departure just won't change anything.
However in the less serious situations brains are working and it's a crowd control incident. The passengers will remember that they had a safety brief so know things could be bad. When the aircraft stops they won't yet realise it's only a bit of excitement. For all anyone in the paying seats knows the clock might well be ticking and it's a competitive life or death exercise. Add a bit of smoke and a smell of burning and everyone wants to get up: sitting still and waiting for instructions isn't a comfortable choice. So need to reassure in an authoritive and calming manner. Like that Glasgow incident, any hint of the word 'evacuate'and the aisles will be full.