ESO U43 136k Arcanist - Runeblades

00:00 Combat
02:42 CMX

cmx images https://imgur.com/a/QhQIKGU

Race: Dark Elf
Mundus: Thief
Food: Lava foot (max stam + stam regen)
Potion: Restore stam, restore mag, heroism
Blue CP: Deadly Aim, Master at Arms, Exploiter, Wrathful Strikes

About setup
This setup revolves around maximizing Null Arca proc damage. Null Arca's ability to multihit in one proc appears to be a bug, but this hasn't been confirmed by devs, and we cannot know for sure if it will be fixed. The set tooltip damage is low - without multihit it wouldn't be able to compete with other trial sets.

Before diving into this setup to clarify on how exactly the multihit happens.

As described, Null Arca gains stack each time you crit, and on gaining 3rd stack it releases stacks to fire a projectile. In fact projectile firing happens 15 milliseconds past gaining the 3rd stack. Every crit in this 15ms delay will cause an extra projectile. Extra projectiles can be formed for any enemy regardless of which one was the 3rd stack procced on.

This means Null Arca multihit can be boosted in several ways:
having high critical chance
using abilities that can deliver simultaneous hits (Forse Shock, Writhing Blades, Inspired Scholarship, Burning light, Elemental/Crystal weapon, etc)
using many DoT abilities so their ticks randomly line up for Null Arca proc (higher tick rate dots preferred)

Writhing blades are perfect tool to proc Null Arca multihits. They have higher crit chance, and most important, deliver their 3 hits in one moment (unlike its animation looks). On top of that they carry Inspired Scholarship ticks resulting in up to 4 simultaneous crits.

Parse rotation

Start at 3 Crux - Inspired Scholarship - Deadly cloak - (walk in melee) Barbed Trap - Languid - Dread - Writhing blades - Stampede - Fulminating - Carve
Keep up the dots, Spam Writhing blades when Null Arca is off cooldown and begins to gain first stacks. Dread has almost the lowest priority, though recast it at least once every 8 seconds for Ult gain. Line up Languid with Off-balance (requires minor heroism).

Opinion on U43 change
Tentacular Dread buff is a small w. It gave around 1,5k extra dps, but nothing spectacular. Still something.

On viability in content

The present setup is otimized for dummy parsing. For actual trials I'd use Coral in place of Highland. The missing crit chance can be obtained with Mora's Whispers + Slime in place of Selene.
For AoE encounters non-beam arc can go with Azureblight, using Coral/Sul-Xan/Depth bow front bar and Maelstrom staff on back. Charge crux with Physical Burst Scribing, and run as many AoE dots as skill bar can fit. It's an untested area, but resulting damage should be at least on par with other classes.