Interesting. As someone who was massively influenced by Famine, Affluence and Morality my hunch is that philosophical arguments are very effective for a small group of people. I don’t think this should obviously cause EA to switch to, and only to, narrative arguments: maybe those convinced by philosophical reasons end up being the more effective altruists.
I was also hugely influenced by a logical argument (GiveWell: we do research, you do none, why not use our research and have more impact?) I suspect EA has a disproportionate number of people who are motivated by argument vs. narrative, and probably underestimates the degree to which narratives can convince a broader audience. (That said, I wouldn’t suggest any major strategic changes as a results of this, or any other, single MTurk study.)