Yes they really should be in the game because they were the predessesors of all more modern warships as the frigates and ships of the line. When they were state of the art they were not slow at all. They were well armed and highly maneuverable warship which were pushed into the trading roll when more modern ships were developed.
An open world game like Naval Action would be totally boring without trading and we dont have proper trading ships yet. I cant imagine to transport cargo in a Victory or Constitution.