This is my attempt to make a lore accurate Witcher in ESO while also still making them viable in PVE Dungeon & Solo gameplay. Both combat bars are built for Two Handed swords fitting the whole Witchers with two swords on their back vibe.
The first combat bar is built around DMG while the second is built around Healing, Buffing, Debuffing & DMG. All of the Healing, Buffing and Debuffing work on yourself for when soloing and on your group for when playing with others. Your main focus is DMG but you can off-heal and buff/debuff your group as needed.

The Class is Arcanist for several reasons, one being that the runes look like Witcher Signs while they cast them. The other being that they had the most spells that matched Witcher Signs.
The Witcher Signs are

"Quen" A protective shield spell. To mimic this we use the the Arcanist spell "Chakram of Destiny".

"Axii" A mind controlling charm which stuns them. to mimic this we use the Arcanist spell "Rune of the Colorless Pool"

"Yrden" A magical trap spell to mimic this I used "Fulminating Rune" as it worked best with the build but also still fit the RP. Some alternatives are "Volcanic Rune" in the Mages Guild tree or "Barbed Trap" in the Fighters Guild tree.

"Igni" is a magical flames spell, This one did not fit on my bars so is not being used. but some good choices for this if you want are "Inner Fire" in the Undaunted tree or "Meteor" in the Mages Guild tree.

"Aard" I telekinetic blast spell, I have not found anything good for this yet... I am hoping when Scribing comes out I can make one.

Witchers also are big into carving runes into their blades and enchanting their weapons & armor. To do this we have the "Recuperative Treatise" spell and the "Crushing Weapon" spell. We also have gone down the Enchanting tree.

Witchers also practice Alchemy brewing potions, poisons and elixers, as well as go on perilous quests to find armor and weapon crafting scripts to get better gear so we also went down Alchemy and Blacksmithing trees.

If you are wondering why we have "Pragmatic Fatecarver" on are second bar it is there to give us some more dmg on the second bar, and help with the overall flow of the build, we have several abilities that build Crux, that is the one we have to spend it. It is also just super fun to use... If you want bonus healing swap it out for Remedy Cascade instead.

If any of you have any suggestions to make the build better let me know, thx.