Athel Yenlui is actually quite easy.
I played during the beta back in February and that was the first map we played for 2 weeks straight. During the beta we could only play Recruit but my friends and I played it so much that we figured out a few tips and tricks on how to beat it.
-Hug the walls: This sounds silly but if you ever played The White Rat on Cataclysm then you know what I mean.
-Stay together but don’t crowd each other: When people bunch too closely together during a horde, then everyone can get downed simultaneously. Stay within a few feet of each other.
-Boss + Horde: This is one of few maps that always guarantees a boss plus horde. Biggest mistake people make on this map is to go full Rambo on boss and ignore the horde. The horde will overwhelm you and you will all die. Have 1 person hold aggro on boss by kiting them away from the group and then dodging around in a semi-circle (prevents you from getting too far away from team). Not too close to where the boss will change aggro but also not too far away to where your team can’t get to you if you get pinned. While the boss is busy, the other can chop down the horde and then assist with boss.
-Event: One person aligns the crystals while the other 3 are in the center. I don’t know if this has been patched but if you have 3 people in the center area, the only enemies that will bother the person aligning the crystals are the few rats that drop down. Those can be sniped by your sniper. Have one person protecting the person doing the event, while the other 2 protects the sniper. Ofc trying to get a PUG to do this is awful. Don’t hold your breath.
When everyone in your group has a designated role, that map becomes super easy. Unfortunately, we have too many greedy people chasing green circles like their lives depend on it so that is why this map is so difficult.
The map is team-oriented so if your team is not working together, it becomes unbearable to play.
Side Note: Have you ever noticed that the person with all the green circles is usually the first one who gets downed or dies?