Is it really a direct competitor though? I mean it is in the "streaming video" sense. But Amazon Prime is not really in the business of producing original content whereas Netflix is.
A relatively large proportion of what I watch on Prime is Amazon Studios content. Largely because there are more interesting series than I have time to watch, and so it's easy to pick the content that's already included in the Prime subscription I'd still have just for the delivery first, and relegate content I have to pay extra for for later (that said, I do end up paying for quite a few movies).