Agree with OP. It is a waste to have so many essential abilities stuffed into the role slots. I've mained a WHM for a long time and looking at that list? What are garbage fire for the sake of symmetry. Basically having to choose all five from essential need. Even if the new content does not require it, the old content does. Queuing up for multiple content selections is part of the game too. So realistically, I think most healers will consider Esuna to be a required ability and, unless constantly switching out abilities becomes a real thing, they will just leave it on their bar. Opinions and meta aside, vast majority of players will probably do this.

Also consider new content. You always have to have it on the bar because you don't know if it's needed or not.