the new trial is too hard

[Zfz]

Beats the hell out of me, but usually by the time we get to the end the adds are overwhelming in number, usually just killing people over and over again that try to get close, and Vishap isn't even close to being dead.

You should not even be near Vishap, let alone the adds. Only the tanks (or even just 1 tank) need to be by Vishap, he can catch all the adds as they come for the healer, if the healer is properly positioned.

Vishap&Adds&Tank-----Healer------DPS&Cannons

That's all you need to do. AOE? What AOE? Adds overwhelm your tank because you're not using the cannons to take them out. Cannons deal 2000 AOE damage per shot. It's far stronger than any DPS is capable of in the game now.

On the run that I cleared it as healer, we had exactly that formation I noted above. I only needed to heal 2 people: regen on the tank and maybe one or two Cures, and another one being a BRD who refuse to stay on the cannons and get hit by adds AOEs as you mention.

The fight doesn't need to be toned down. You're just doing it wrong. What you're asking for, is to break the fight so you can complete the trial using your wrong methods. It's like asking for the last boss in Tamtara (normal) to not go invincible when Imps are up because you don't want to kill the Imps.

But the best way to do the fight is to have all 4 DPS on the boss, one of them will be on Dragonkiller duty but the other 3 should never stop hitting him.
1 tank and 1 healer should be on cannon/snare duty since you don't need them both to be tanking/healing. Leaving the DPS to wreck face.

DPS whacking on the boss behind the boss means tanks have to move around collecting adds. Extra healing pressure with DPS who can't avoid AOE or who are so trigger happy they just have to put AOE on the adds (hey look at my meter I top the charts!) Extra healing means extra enmity so tanks have to spend extra resources maintaining aggro...