How did United States Civil War-era frigates compare with their contemporaries?
Short answerThey were adequate and useful in numbers, but an American frigate would not want to fight a ship as powerful as HMS Warrior.
NotesThe Civil War-era American frigates were competent rather than exceptional. Their program emphasized putting useful numbers into service more than creating a single dominant ship. Against most contemporary opponents they would still have a credible chance. HMS Warrior sits outside that comfort zone because none of those frigates would be an attractive opponent for her.