I kind of like the idea this presents.

Let's spin it a bit further though.

Give each class a unique challenge objective.

Tanks: focus on agro control and timing of defensive skills to mitigate damage while npc assistants dole most the damage.

Healers: focus on healing said npcs while maintaining damage and keeping your npcs alive.

Dps: Focus on dealing damage to avoid npc tanks from falling in battle and avoiding damage themselves.

Make these easy to access and offer unique rewards per role or job such as titles. I'm sure if it was engaging and not face roll-able it could go a long way to being a good stepping stone for players to challenge and better themselves.