This same kind of advice can be used for any kind of writing that doesn't fall under pop culture. Basically anything that isn't Star Wars.
In roleplaying its nothing new to stat out a monster but it may not of been an avenue you've tried when trying to write the settings fluff.
This lack of description becomes a larger issue when you have spawned a new breed of monster. When you say dragon, I know what you are talking about. At the very least, I have an idea of what you are talking about. But if you go springing an ancient force hell bent on sucking out my eyes and using my spine as a fiddle bow, then I need to some details.