The best elemental lategame mage build I used was actually 5 in all elements and poly + a little bit in scoundrel (with gear of course) + glasscannon. Then you can spam max tier source spells under apotheosis + adrenaline (potentially recharging them with skin graft in the end), and they do way more damage than anything else mage has, even when compared to if you had 10+ in the relevant skill. You also usually have at least some spells that would hurt. Still this is weaker than a maxed physical build that also requires no skill to build or play.
... I'm pretty sure that all optmized characters will have access to Adrenaline, Apotheosis, and Skin Graft at minimum - +10 anything will have enough points for that. The rest comes down to gear available and then you specc accordingly.
