You got it all wrong.
Grisban can't get rid of immobilize or stun with his hero ability and it's imo the weakest hero-ability in the whole game, as you recover your fatigue at the end of your turn, not immidiatly when taking a rest action.
If you are stunned, the first thing in your turn you have to do is to get rid of stun with an action. You can't rest first.
Note that Grisban can only get rid of a condition when recovering fatigue from a rest action, which will be on the end of a turn. He doesn't get rid of conditions when taking the rest action, but only when it's resolved, at the end of your turn. By that time wether stun nor immobilize has an effect on you.
So in my games Grisban basically has no hero ability which is extremely weak AND he has only 3 movement points (that is admittetly not so much of a problem in act II). I think only one of these drawbacks would suffice to balance out his 14HP but apperently not.