They both have the legs to run down their respective touchlines still. I guess I just meant when you have Tomori and Christensen on the bench you don't really need to put Azpilicueta in a CB spot. It's like putting Fernandinho at CB. He can handle it but it hurts the team.
Maybe Frank is trying to do a Sheffield (which would be really cool actually) with the overlapping wide CBs. Needs more time to develop though.