There is no logic of what you said about Fabinho seriously. You don't even give me a proof if midfield is his favourite position or he wants to settle his role as a midfielder.
So if you say something means it's true??
Young has been our regular left back this season and top 3 or 5 of our best player this season. Not sure how you can argue with that and said that he can't nail down the spot. And now that we have Shaw is being pushed by Mourinho & Young's performance and started to show improvement, I don't see why can't we just keep trusting the left back spot to Shaw & Young for at least one more season.
I want to buy another player in right back role because we only have Valencia who is good enough for that role and he's going to turn 33 years old this year. While in left back role we already have two players who have showed that they are good enough. Why can't you understand this?
Alexis has been playing on the left in Arsenal, he also can play on the right. Alexis also played as a striker most of the time last season and scored 24 league goals. And Rashford has been playing on the left & striker.
If you want someone to backup Matic and don't mind to be bench warmer, we got Herrera who actually played very well in Matic's role last season. I even shout Fabinho who is versatile & can play in two different position as well. Less money to spend & less time to do business for one player than two players, and less rotation which allow Mourinho to settle his XI.