It all depends on the level of difficulty they're aiming for. Difficult and challenging for the average player? For the hardcore player? For the top 1% of players? It's doubtful it will be the latter or even the middle option because they want content to appeal to everyone and this is the first real content they're adding. They will want the average player able to beat the content even though it's difficult and challenging for them. Problem there is the top 1% won't find it as difficult and challenging as a more casual player therefore you can get away with doing it with a man or two less. Additionally the hardcore and top 1% of players have more classes ranked up, more cross class skills, more HQ gear etc. and this too reduces the level of challenge.