I would add to Warpig's build the following adjustments:
- Swap out Bound Aegis for Twilight Matriarch
- Swap out the destro ulti for Energy Overload, put Power Surge and Boundless Storm or Dark Exchange on there
- Replace Power Surge on the back bar with Daedric Prey
- 600cp should be 100 Ele expert, 75 Thaumaturge, 15 Elfborn, 10 Spell erosion
- Double lightning staffs
You will find all of the easiest combinations and a full run here:
https://forums.elderscrollsonline.com/en-GB/discussion/comment/3904371#Comment_3904371
This build (with a few variations depending on preference) has become one of the most popular ways to farm the arena.