Yes he is inderperforming lol. Have you seen him? Adds less and less every time. That's his trajectory every single time. Season starts, his talent and promise show through his technique, gets starts and everyone is hopeful, quickly becomes useless guys the bench and plays less and less.
He is a central midfielder whose main contribution are runs into space with the the ball. At everything else he is average or below average. His apparent talent never actually shows in consistent performances.
He is obviously behind the 3 starting midfielders, then behind Isco, then behind Asensio and Vazquez. Soon enough he will be behind Ceballos.