Some novelists write with great precision: think of the restraint of Henry James or Gustave Flaubert, who seem to choose and place every word meticulously.
And some writers impose rigid structures on their works: think of The Sound and the Fury (though self-imposed structure is the only thing that could contain Faulkner's overflowing waves of words).
When I read Dostoevsky, I see neither precision nor structure. But the reason is simple: his characters will not allow it.
In Dostoevsky's novels, characters reach into their chests, rip out their hearts, set them on the table and shout, "There, look at that!" Characters are suffering in their souls, and exposing their souls. The words "restraint" or "manners" suit very few of Dostoevsky's major characters. They are all mad, talking, talking people, running about consumed with ideas. The ideas are so overflowing, the characters so eccentric and so full of passion, that they cannot be drawn with precision but only with energy-infused words, and they are too big and unrestrained to fit into structure.