The reason Ponga is so skinny is because he hasn't done a pre season the last 2 years. Was in hospital in a life threatening situation and still carved up 20's later that season as 17 year old.
He is actually a lot stronger than his body looks. Will be breaking a lot of tackles when he adds some more lean muscle to go along with his footwork.
Cowboys will have a plan to keep him, they always knew he was coming through and still signed Coote so am sure they know what's doing.