Individually he's a good defender its positional sense he has problems with sometimes but i'm quite confident that will come.
How many fullbacks are the finished article at his age? most fullbacks reach their peak around 26-28, Baines for example wasn't half the player he is now at Santon's age.
Also needs Jonas to hold his hand apparently
He was up for today thats for sure. He just needs to continue to work on his decision making in the final 3rd when he's bombing down the left. He tends to cut in and do a little hop into a player and boom they counter and he's caught out.
He fixes that side of his game (over time) and continues to craft his defensive side - then hell, we have a top top player that everyone saw could develop into when he was putting in ridiculous performances for Inter before he fell out of form