I think you are being a bit harsh to say Alzate was struggling, for me if was more of a case of Propper is more effective playing central and Alzate more comfortable with some width. Good change by Potter in my books.
Potter shows a lot of faith in him. Clearly believes Alzate is versatile enough to flex with his change of tactics. Seems so composed and calm on the ball - always an out ball to him when needed. I suspect he'll eventually replace Stephens.