Plagues and other great diseases are important parts of history and some settings. They defy man and may even defy God in their swift and terrible punishment upon the body of society.
My issue with modifying/removing dwarves and elves is that the PC’s may want to play them.
One of the most powerful tools found in the World Building 102b article is the Worksheet. Here is a place to put the settings you might make with them.
"Ladies and Gentlemen of Worth, please come closer and have a look... " In a little stand with numerous maps, the human Advantos sells land-rights with a shining smile and jovial talk at bargain prices. He sells even squatter rights (first to settle is the owner). About 20% of the lands do not exist or belong to someone else. About 30% do not have even that value, or have other problems attached- swampy, cursed, haunted, Old Indian/Pet Cemetery (tm)... Be assured you will not see this man in the same city twice.