Yesterday, I wrote that product managers should not rely on SMEs as their primary source for requirements. I will now go further and state that, to the extent that a company hires a product manager or business analyst to interact primarily with SMEs, the role names "product manager" and "business analyst" are misnomers.
I see this problem often in companies. They believe they already know the requirements (often confused with design); they are just looking for someone to document them so that developers can get to work. They call the person who does this documenting a "product manager" or "business analyst", but this person in fact has only a small - and very tactical - subset of the responsibilities that these roles entail.
In my opinion, this problem is largely responsible for the misconception that SMEs are primary sources for requirements.