The storm carl is a very physical career and therefore suited two combat abilities. The reaver also has two combat abilities. As you rightly point out, they do not benefit from your brawn, therefore they are balanced. However, both abilities ignore armour. Hurricane rush is an excellent 'finisher' ability. If you have multiple opponents on low health (particularly in combats where opponents are being summoned or spawned), then hurricane rush is a good means of picking off a load of weak opponents - potentially also triggering a death move. Not every combat ability should necessarily be about hitting huge numbers. Wave is similar; an ability that gives you control over the weaker/damaged opponents you may need to pick off.
Yes, you are correct in your assumption. Hurricane rush is a bit of an odd one in this context, but you roll the dice separately so if you were to use critical strike, the critical strike would apply to one pair of dice as they are the only ones in play at that time.