In 2019, a small group of enormous real estate deals, while bearing little relationship to the overall market, had an outsize impact on the national conversation about wealth inequality and the rapidly expanding billionaire class.

A boom in ultrahigh priced deals in Palm Beach this year, including the $111 million sale of an oceanfront estate, raised questions about the number of wealthy New Yorkers fleeing to Florida in response to a 2017 change in federal tax law. A string of $100 million-plus deals completed in Los Angeles...