How does the game determine whether the tank turned the boss towards the group and the melee got cleaved, or the dps ran in front of the boss to get cleaved? Whose rank goes down? How does the ranking system take into account tanks who move the mobs out of AoE or constantly spin the boss?

Does the tank get a lower rating if he goes in dps stance? If not, then how is a tank penalized in the ranking system if he focuses so much on dps that he doesn't hold aggro and other people start to take damage? Will dps be penalized for not using enmity reduction skills?

Effective healing is the same as party damage taken if you don't take into account self heals and passive regeneration. Is it fair that a healer gets a lower ranking if there is less to heal in a good party where stuns are used and mobs die faster? I think not. And who gets penalized if someone dies? Sometimes it's the healer's fault but sometimes it isn't.

Does the system recognize and reward the dps when they focus down priority targets (like bees) instead of padding the meter with AoE dps?

Are people going to be rewarded when they interact with objects to advance the fight and lose dps in the process?

If all of this is not taken into account, then we will have people getting annoyed not only for having slow runs sometimes but also getting their grade ruined by their party members. I'm still not convinced that a ranking system will ever be accurate in this game. They could implement it for fun I guess, but I wouldn't want any cosmetic rewards to come from it.