"Did you find the portrayal of the British in that film to be a bit rough?"
To some degrees it was accurate, but in others no, it wasn't. It also soft shoed to some degree the actions of the Americans.
The War in the South was an ugly, ugly thing, FAR worse than what went on in the North.
IIRC, the movie takes place in 1776-1777, which is several years too early for the war in the South. The British didn't start focusing on the South actively until 1779 or there abouts.
Col. Tavington (I think that's his name) is fairly closely based on the (supposed) actions of Banaester Tarleton, who is said to have committed atrocities against American troops who were trying to surrender. There is no evidence that he ever committed atrocities against American civilians. Likewise, there are a number of scenes in the movie (the church burning, for example) that are pure hogwash.