If you put Pellistri in Eredivise and make him play 80 games per season, being crucial player, getting a lot of assists and goals, refining his game especially in the final third, decision making, rising his fitness etc. By the time he might come back he would still be similar age as Gakpo or Antony. It isn't as bad place for loan as it may seem, not every loan ends up like Amad.
He needs to play as much as possible after his failed loans, where he's been frozen by manager only used as a back up seen not good enough.