Exactly right. People like to ignore all the factors that lead up to the shooting so long as what happened IMMEDIATELY prior to it make the shooting justified (in this case, assuming the guy did grab one of the cops guns). It is likely the situation could have been handled where no violence was used by anybody and no opportunity would exist for a cops gun to get grabbed.
Here are two police shootings that I think given the circumstances, were justified, though those circumstances were at least partially the fault of the cop in the first place.
Though the guy wasn't cooperating, he wasn't fighting the cop. The cop decided to escalate it by kneeing him in the head. Predictably, the guy responded back. The cop decided to get himself into a one on one wrestling match and was losing badly. He put himself in a position where he had little choice but to shoot or get beaten to death. The whole thing should have never escalated that far.