Giving them a weapon would need an entire new set of animations as the ones they use now is for hand to hand. Using the xivilai's would have them fight upright (man-like), it would mess with their natural beast stance. And they would have the weapons in their hands while moving around, would look like

Beside these don't need weapons. the spikes are big and deadly enough. Wait till you have an armored troll with these gauntlets swing at you.
I will build 3 types of armors for them based on what you saw already. this is the near final of a full armor. others will be a bronze/copper version of it, and a non-spiked, clean looking one for the imperials trolls.
here's an image explaining more...
