WHM getting progressively more unnecessary in content?

[Yeol]

Think of WHM as the MNK of healers.

MNK: Great dps numbers on single target.
WHM: Great healing potency overall.

Both of these jobs lack utility. Not every job in this game should have utility. Some people prefer to be pure healer, pure DPs.
Being overpowered + having utility is just not right. Why would people bother playing other jobs if they have a very powerful job that has everything?

All healers are balanced, and all of them can solo heal content.
Some can do it easily and others have to work harder. In the end, all of them can do it.
It is up to the player and their skills, how they play around with the tools given to them in order to achieve something great.

A group with WHM/MNK can still clear content. They are not really useless or less powerful like what you seem them to be. If you want to have utility simply change your job.