The level 80 quests doesn't reward you with any skill this time around.
And as Fal_Kearst mentioned, the quest is referencing Shadowbringers' story. + considering the events of Shadowbringers, it wouldn't make much sense in the storyline to allow you to do that quest IMO.
It is basically the same reason why you need to complete the MSQ to do any type of end-game content in the game.

I don't think there is a reason to be angry about questlines being tied together a little bit more than they used to when the reward is just the quest itself and the title that you'll get anyways as soon as you actually do some level 80 duties.