You keep repeating that Davies is a CB/LB. He isn't, He's a LB and occasional LWB.Davies is a CB/LB so playing him at CB makes sense. It is t randomly throwing someone into a position, it is playing someone in a position they are very comfortable to play in. It makes perfect sense.
We tried Son as LWB a couple of years ago and it was a catstrophe, as was Skipp out wide on the left - he barely touched the ball!
Now get back to your Playstation and consider playing Lloris up front and Harry in goal.