That’s the wrong argument to make IMO.
Cancelo is a top class LB and I don’t think anyone should have any worries with him playing there.
The issue is the lack of depth at full back. As it currently stands, we are an injury or suspension away from playing an unproven kid or a player out of position at full back. And with Walker getting towards the end of his careers, it’s not an ideal scenario.
I understand that Stones can play RB and Ake/Laporte LB but no one can seriously suggest that we look a stronger, more fluid side with them playing there.