Yes, the House of Grief was difficult for me too (on Tactician). Shadowheart had to use her special one time only divine power to let us gain the upper hand. It made me reconsider my 'please add another difficulty level' viewpoint.
The difficulty of boss fights is probably personal, and depends on how well your party can counter special boss powers. The party that I brought to the House of Grief was getting complacent, did not pay much attention to being prepared for all circumstances. I very much liked how the game showed me the error of my ways.
Think of it this way: would the game be more fun to play if the act III boss fights were made similar?
