I really don't see any GM waiving a player they just got in a trade before he even plays one real game for us. Especially after talking him up as an asset
The correct move is to let Sbisa play for a while and see if he can improve his game.
GM's who make knee jerk reactions on the basis of one pre-season game don't deserve their job. Benning knew that Sbisa would take some work when he acquired him. He'll wait to see if he can improve his game before getting rid of him. As any competent GM would.