Brand advertising efficacy is notoriously hard to measure. Where does the data come from to support the notion that FB excels at it?
I've seen a ton of ads for Snorg tees (for example), and while, yes, that has created brand awareness in my head it's not worth anything until I buy a t-shirt.
I think because people are measuring CPC/Ms, conversions, and basically using this as a lead generating tool, they should be trying to work on that aspect of it.