By that logic we don't need to sign players for any position as we have players capable of filling in.
Smalling, Jones, Rojo, Bailly, Lindelof, Tuanzebe and Darmian can all play at CB so no need to sign a CB.
Pereira, Fred, Pogba, Mata, McTominay, Matic and Gomez can all play CM so no need to sign another midfielder.
Our side is terribly unbalanced, whenever we play the likes of Mata and Lingard on the RW they meander all over the place and don't keep the opposition left back occupied. Which leads to our RB getting double teamed again and again and they end up just sitting back and not providing any width on the overlap. It results in us having virtually zero threat down one side of our team.
No idea if the stats are available but I would love to see how many of our goals over the last 5 years have came down the left as opposed to the right. And how many of the goals we've conceded have came down our left.