I’ve finished all the campaign quests, playing on tier 4 now and the echo of hatred dungeon isn’t spawning and it says I need to do more campaign quests to get to the Dark Cathedral. None of the other endgame boss dungeons are on my map either.
I’m at the same spot as you. I believe both Echo of Lilith and Dark Citadel are only available in torment tiers, but they failed to explain this in-game…
To get there, you need to finish a Tier 20 Pit.