I am playing this build in Tactician right now with a double mage party (Jahan being one of them), both using the 2x wand build, a Cleric sword and shield + tank build, and Bairdotr as her base marksman build.
My two mages control almost every battle. Every fight I've gotten into in Tactician mode has been a breeze.
For example:
First try Braccus Rex fight - beat it with no deaths, hardly took any damage either, using clever sneak positioning with Bairdotr to one-shot the Galvanizing/Immunity Aura totems and the mages with WATER WANDS, which destroyed everything in that fight no problem (A lot of people mention how tough this fight is in Tactician - it was extremely easy). Twins-by-fire-joined got Two-shotted by water wands... everything else there is crazy weak to water damage and were done before they could get an attack out.
The dual wield wand build works not only with Witchcraft, but with hybrid elemental mage builds as well for some of the same reasons Dirtmagurt stated.
You don't even need to invest the full 5 points into Dual Wield to be able to use them to their fullest potential. You can go +4 Wands base and get the additional skill added by your chest armor, and +4 Dual Wield (+1 Added by Belt) which leaves you 10 ability points to spend elsewhere, like on Body Building or Willpower later on in the game (which are also undervalued but hugely beneficial). And you'll still have enough skill points to use two spell schools at level 5 and apply a vast number of points into other abilities as well....
Another benefit is the Leadership ability - an ability that a lot of people undervalue but is so ridiculously overpowered that it's almost not an option in Tactician. If one of your main characters has the Righteous trait, you can get +6 leadership on him/her by dual wielding +Leadership wands, using a +Leadership helmet, +Righteous, and investing only 3 ability points (Level 2 base) for level 6 Leadership.
Wands can also get +3 CON or +3 Int as well, makes them insanely viable to re-stack health if you want to go Glass Cannon, or do more damage with your spells, though I prefer to go +3Con/+3Con every time. I end up with more health than if I go +Speed/non glass cannon using Daggers to get the AP (due to not having to waste enchantment slots or base attribute slots into DEX to use daggers). Which allows me to add even more CON or INT into the build via base points or other items and more AP per turn.
You can also get pure Tenebrium damage wands, and in late game they will end up doing close to the damage you can get on a crafted superior daggers. Most enemies don't resist Tenebrium, even in Tactician mode.
On top of that, Wands can crit where spells cannot. And they are ranged which keeps your spellcasters who use them away from the fray while designated tanks help control the battlefield with knockdowns and Taunt. And they are not limited to using their attacks once per turn like "Staff of ____".
If you ever find that your enemies are completely immune to Elemental damage (in Tactician this is very common), Tenebrium will destroy them. In early / Mid-game - What's more is that if you reverse wand damage type from your elemental spell damage type, you can basically ensure that any spellcaster whose spells are rendered useless due to enemy immunity, will still remain incredibly useful in a battle (Using Water+Air wands duo with a Pyro/Geo build for example, or the opposite - using Fire+Earth wands on a Hydro/Aero build).
I'm sure I'm missing something as I typed this rather hastily to head out to the store before it closes. But I hope this helps.
