Basically everything is good ingame. All you need to do is grind.
The best ingame way to use Aurorus is probably going to be abuse of what is basically STAB Hyper Beam. Hyper Beam might be an awful competitive move, but ingame it is useful since it is a 150 Base Power attack. Ingame options allow you to switch out your Pokemon after you KO, so Hyper Beam is a great finishing move.
As for its competitive use, I'd agree with you. Rock/Ice gives very few nice resists, and a ton of horrible weaknesses. Considering its stats are more of a tank than a sweeper, this is fairly crippling. Especially with Fighting being such a huge offensive typing. It also doesn't have the greatest movepool (with the possibility of being the only Gen VI Pokemon with Stealth Rock the only thing of any note.) It has nothing to really abuse Refrigerate with in competitive, and Snow Warning got a significant nerf.
