I think that is an absurd opinion, can you please tell us why you are 100% sure that he never will be world class? He is one of the best players in the world in his age group, and has every chance of becoming one of the best players in the world. At the age of 19 he has been a key part of a title winning Benfica squad that made it to the quarter final in Champions League, and featured in 6 of 7 games as he won the Euros with Portugal. He has even showed abilities that made a sensible club like Bayern München potentially break their transfer record in order to get their hands on him. Very, very few players have done that much at the age of 19. He has achieved far more than the likes of Pogba, Suarez, Bale, Aguero and Griezmann had at his age. You can't seriously mean that one bad season in a new country with limited game time and problems adapting to the new culture and language is enough to transform one of the biggest talents in the world of football into a hopeless player that will never become world class.
Just look at Mbappe who has been absolutely on fire this season, and is on everyones lips. Give him a season at Real Madrid where he hardly plays and has problem adapting, and you will see how fragile a player is at that age. But the fact that you are not performing week in week out at that age, does certainly not mean that you have lost all you abilities as a footballer over night.