As to brutality, I won't comment. I do strenously object to the numbers hinted at by "a large percentage of the population of the 13 colonies fled to avoid being brutalized." Estimates of Loyalist sympathy within the 13 colonies are usually about 20% (of a total population of about 2.5 million). The total number of colonists who actually fled (not including "Black Loyalists" and displaced Indian groups) is about 45,000-60,000, about 10% of the total number of Loyalists but only 2% of the total population. Including the freed slaves and displaced Indians, you only get about 100,000 or so.
That's true - the number of Loyalists who actually fled to Canada was pretty small compared to the total population of Loyalists, let alone the total population of the colonies/USA. I think that the ones who fled tended to be the most committed Loyalists, who had strongly supported Britain and often fought in special loyalist regiments. Most of the Loyalists whose support for the British cause was less intense and more passive usually stayed in the US and reconciled themselves to the new state and national governments. Some states passed harsh laws confiscating the property of all loyalists, but it quickly became obvious that many Loyalists were economically productive citizens and that states would be hurting themselves by forcing them to leave. Most of these laws were repealed within a few years.