The Orc racial simply helps you level heavy armor faster. Ultimately, it gives no benefit to wearing heavy armor.

Assuming you are creating an Orc mage for PvE, I'd go all light armor. The magic armor bonuses are much better for a mage in terms of power and sustain than the bonuses for heavy armor. Heavy armor bonuses help survival, but the sorc's class kit includes loads of survival skills that are fed by magic - which is helped by light armor.

With costumes and the outfitting system, you can make your orc mage look just about anyway you want. You can make it look like they are wearing full plate armor if you wish regardless of what they are actually using.