If you watch Mbappe very well when he was playing for PSG you actually know that he is a good player I think he's just having a bad season in Madrid because of the little adjustment in the team and currently he's still trying to adapt to the playing pattern of the club
and I think he will get better very soon and the goals will start coming. The position of the player should be decided by the coach not us if the coach feels that Mbappe can't function well from the left wing then he should make the change and make his team to function very well. Right now I think it will be difficult for Mbappe to be seen as a great player when Vini Junior is still there I think the co-operation will not work until the manager steps in.
It reminds us of the situation where PSG had Messi, Neymar, and Mbappe in attack. they are players with goal scoring characteristics, we could see some times their partnership did not work well but eventually, they looked a little better.
The same thing might happen in Madrid now. Mabappe has to learn to adapt to the current team's game. and Mbappe's current position is as a center forward. right now he is not good, but we might see him more productive in the future. if he still fails this season, we will see next season if he can shine.