How should they address the disparity within the role?

[GrimGale]

healers should have more different/stronger niches

To have "niches" you need gameplay variability. All of the encounters are mostly "move here then here", "hit boss", "restore HP/mitigate"- There are no other meaningful mechanics beyond do the dance and mitigate then fill bars up. No status effects, no CC, no unique buffs to apply or debuffs to handle. Utility and its niches have been steadily been removed- You can't have uniquely designed jobs because the game has been designing them away in order for every job to be able to tackle all the content.