They are progressive power metal buddy, when a site reviews an album they don't lost every genre, and by the way AMG lists kamelot as heavy/death/black metal so who cares what you found on some random webpage.  The fact is they are progressive.

As wiki states prog metal is "Progressive metal is a genre of heavy metal music which shares traits with progressive rock including use of complex compositional structures, odd time signatures, and intricate instrumental playing. The high level of musical proficiency is often combined with a lyrical counterpart in the form of epic textual concepts, resulting in lengthy songs and concept albums. As a result of these factors, progressive metal is rarely heard on mainstream radio and video programs, much due to that the length of the songs are not suited for those medias."

Kamelot meets most of those requirements, to deny that they are prog is to deny them what they are.