In this case, I think they are referring to the fact that Crota's End Hard Mode enemies are 33, while players are only able to hit 32. Thus, we have a damage reduction due to being one level lower than the enemies. With the House of Wolves, we should be able to hit at least level 33, making us the same level as the enemies in the Crota's End Hard Mode Raid. So it actually makes sense that Hard Mode will get a little easier. (Assuming that the Hard Mode Raid stays at level 33.)