23 is young for a footballer and it's first full season with us, same as it is with Dalot and Fred. Writing him off is daft because the PL has proven time and time again that the step up for some players takes longer than others, especially since he just came from La Liga which is a naturally less physically-demanding league.
You're right, not all academy players have it, but Pereira has always been one of the more talented players in his age group since we signed him as a kid. He showed enough at Granada and Valencia to show what he's capable of, he showed plenty of improvement while on loan too, so much so that both clubs wanted to sign him. He's more than capable of being a squad player here, it'd cost more to replace him than keep him in the current market.
As for the point I've highlighted in bold, what on earth are you on about? Again, this is Pereira's first full season with us.