I’m currently following this build, but it’s theoretically a support build, not a damage one. Wiz3 - Ele3 - Warlock or Wiz 3 - CryoPsycho - Rune Caster combo are the attack/CC ones.
For Thaum3 - Rune Caster, you are looking at buffing the whole party with raw attack and defence power: Swell buffs, Shrink debuff, Lethargy attribute, Rune of Ice. Wiz 3 Quick Cast has synergy with Rune Caster, in both cast time and burst damage. Rune of Giant fits well with the build’s high CON (high INT + Transpose) but limits what skills you can use.
For damage, auto atk is slow without a Chrono, so expect to use Sleep - Quick Cast - Magic Missile (bounce missile) and Rune of Destruction (attack every mobs within an area) or Rune of Justice (a multi-hit straight line). For CC, Energy Bolt (AoE pushback) and Earthquake (AoE knockdown). Not enough to kill, but suficient to keep yourself safe.
Edit: Totally forgot about SP issues. Some Thaum buffs are SP extensive, and by the time you buffed up (around 450 SP for all Thaum + Rune Caster buffs), you may short on SP for attack skills (300 SP for Sleep combo and Rune of Destruction), not to mention rebuffing. You have around 1k7 SP with 8 SPR at lvl 200, btw.