Dev's decisions (mainly healer part) are not from the feedbacks from players
They do whatever they feel is right.
They do not play as healers for sure.
They also don't want to put budget into the healer design because healers are not as cool as melees. Cannot bring them profits by attracting new players to play this game. (in their eyes) that's why all the cg trailer has to be a non-mage job as the main character.