You call it waste his productive years? There is a team Nico Williams will go now and his career will nosedive because he will be moved to reserve due to the presence of equal or better alternatives. Instead of going to Barcelona or Bayern Munic where he is not sure of playing 20 matches in the season, it will be better for him to remain in Athletic Bilbao and continue enjoying the attention there. You already knew he is young with plenty of years to still play football, nothing has spoilt for him yet.
Man, just think about it. If you were in his place what would you do? Wouldn't you like to play for a much bigger team in your young ages already? You have already proven your talent in the end.
That contract he signed until 2035 is just absurd. We all know his dream is to play for Barcelona. To perform side-by-side with Yamal... If Barcelona manages to handle this registration problem I believe they will get him sooner or later.