It wasn’t so bad when the game had only 9 hero classes. I could have one of each and there were still plenty of room for duplicates to implement some weirdo party compositions for fun. Now there are 15 hero classes and the number of insano party compositions has gone way up, yet the hero barrack space has not been scaled to compensate for this. It’s immensely frustrating not to be able to do all the All-Houndmaster, Jester-Robber Dance Party, Crusader Train, Abom-Abom, and other weirdo party composition in the game without throwing heroes into the Darkest Dungeon for the torch mark for more space.
You should scale hero barrack space to the number of hero classes available so players don’t have to start new campaigns just to have the space to play with new party compositions.