"Exempt of one management", you make it sound so fair while everyone every role is already exempted of this kind of management while the boss cannot be targeted or is invulnerable. I believe the complete opposite is in practice here: punishment

If healers outhate tanks while the tanks can actually do somethint about it, then yes, make use of those enmity modifiers. But with (extreme long) transitions good for 2-3 minutes and a good chunk of healing is required, it is starting to gravitate towards the unfair side. Or in your words: dps and tanks are exempted of enmity "management" while healers have to keep doing so on the boss.