Only way signing a left back makes sense with our current squad is to sign a kid like him and leave him there for another year then he comes and takes another year to learn Peps methods.
It's easy to say replace mendy but if we bring in somebody who is going to be fit and vying for a place every week it becomes significantly harder to keep everybody happy.
We currently have the options of playing cancelo laporte or ake at left back, that helps to make sure both right backs and 4 centre backs are happy with their game time, add another left back and you take away most if not all of chances to play any of those mentioned there and you risk making upto 4 other players unhappy with their gametime.
May sound daft but mendy being unreliable/out of favour as our second left back is secretly a blessing in disguise in terms of squad harmony