Robertson could easily show up on the opening day roster. The Cardinals have history of fielding guys who are not ready for MLB. Walker, Winn, Liberatore, Pallante, Rom. Certainy , there is no reason to think that establishing dominance at AAA is a requirement. Robertson would be way cheaper than hiring someone qualified for the job. That doesn’t mean it is impossible he would be adequate. Look at Mercado and Palacios, both hired to fill th same role. Of the two, Palacios did quite well and stuck, as unlikely as it seemed when he showed up on the roster. You just never know.