The chances of anybody doing the same type of EE are you are fairly small indeed - and nobody else is going to have any knowledge about this area unless they are! This is what the EE is meant to teach you - independent research and learning where you're just as in charge of research as everything else. I suggest going on google scholar and seeing what you can find. And as for making it argumentative, you need to set yourself an argumentative question! It's as simple as that.
"conceptualisation, identification and treatment of mental illness in the Ancient world" = description of random facts
"How does conceptualisation, identification and treatment of mental illness in the Ancient world differ from the modern day?" = way too big a question for an EE, but at least it's a question and not just a load of factoids
That's how you make your essay more than just a narrative - don't set yourself a narrative in the first place. If your EE title doesn't make you argue a point then it's a lost cause from the get go.