It's not a matter of difficulty.
The more people know a specific piece of content the better they play, and the better they play the less you get to play Healer. And when you're not playing Healer, you're playing the Job as a DPS... And Healer DPS gameplay could be done by this
They could either make the DPS portion of the class better, or give them something else to do when not healing as the way they create fights the only conclusion I can make is that developers don't want healers to heal.