TL;WR: Has anyone done this successfully? If yes, how many players? Any mechanic other than the obvious?
We were in the Domain of Vabbi hunting some bounties when Serpent's Ire came up, so why not do that one since nobody ever did it. Our ragtag crew of nobodies gathered via LFG, about 20, set out to conquer the brand.
Killing veterans was pretty easy, even though a few heroes were zapped by the lightning. Fun times! Then zealots started to spawn. While tracking them down was fun at first it became a bit tedious since you had no idea where to look for them. Maybe they should be marked on the map even without someone close. We found the last one only a few minutes before the time ran out. With 5 players they went down pretty fast. Probably 2 minutes to kill one. So we started to feel invincible!
I also found it quite hilarious that the evil djinns moved the protections bubbles around randomly which sometimes got unaware players killed by lightning.
With all zealots dead we rushed to the next event in the northern area where you had to fight all 5 of them. Only to hit a wall there. Obviously you need to spread out to all 5 and either break their bar often or kill them fast enough before the ritual completes.
It was impossible to break just one bar or kill one zealot. Even with heavy cc builds people brought to the fight. Moa signet didn't even put a dent into the bar, probably removed 5% or something. And so after 2 minutes or so our heroes met their inevitable end.
Is there something to this event we missed? If so it is not communicated well.
Right now it looks like the 5 zealots are scaled for all people in the area but there are only 1/5 of them fighting/breaking each of them. Short of bringing a giant zerg I didn't see an alternative. Which is kinda misleading since the events before that can be done perfectly fine with 15-20. So it feels like that either the event where you need to hunt down the 5 zealots needs a massive scaling up so that it needs a full squad already or the final event needs to be tuned down so that it works with the same amount of players as the one before.