...yes, he looks ideal for a back 3 but I also have doubts about him as a conventional CB. He might have the quality and class to manage that position, after all Ratcliffe wasn't tallest but he was built like a middleweight boxer.
There seems to be growing overtures for Matthew Pennington to be involved and many suggest he's a 'Jagielka type'. If the strategy is a flat back four, Pennington might be competition for a place. Time will tell.
Mason will be fine in a year or 2 when he fills out and maybe bulks up a little, hes got the talent, but hes a bit unpolished atm, as you would expect from a 20 year old learning the game.