People would argue, and even you, that if you're a player in the AHL, for better for worse, you could probably play in the NHL. In a perfect world, Grigs should be in that group, in the AHL.
I do agree with you in not playing him with horrible players. He won't grow. Play him on the 1st or 2nd line. Take a player, no matter how good, that had no future with the Sabres and replace him with Grigs.
Plus, he won't be the only underachieving Sabre playing with boatloads of potential (see Omark).