He's a good prospect, better than Cahill in every department.
He's made mistakes in big games though, awful pass error v Barca. Should have stayed down motionless after head clash with Lukaku, naive to stagger on, lost Lingard for second goal.
Very inexperienced, so mistakes in pressure games no surprise. Hopefully won't harm his development.
If Luiz hadn't fallen out with Conte after the Roma game he'd mainly be a backup. Luiz was superb last year, born to play in the centre of a back 3. Luiz Didn't make mistakes, has experience, superb distribution from deep.