De Ligt is a couple of years younger than Gomez, which is significant at their ages. However he will never have Gomez's pace and last I saw him he still required significant improvement in his reading of the game, which is essential for him if he is to make up for that lack of pace.
De Ligt could become all that he is hyped up to be but equally he could become the Dutch Maguire. In contrast Gomez has already proven himself to be a top level centre-back; if he continues to improve he will be scarily good.
My only concern with Gomez is whether injuries will continue to hamper his career, would hate to see him end up like Agger.