De Ligt can be part of a great defense in my opinion, one that can even rival Arsenal's current backline.
He just needs someone next to him who has pace, can deal with any player 1v1, and can eat up ground quickly. Martínez is not good at any of these things, and de Ligt wasn't made for this either. Yoro is, however, and the only thing that could make him a better partner for de Ligt than he already is in theory, is being left-footed. But he's just 18, and I expect him to be quite raw in his first 1-2 seasons.
My issue is that Maguire is already capable of doing 99% of the stuff that de Ligt does. So why not sign a wide defender like Branthwaite and put him next to Maguire, to create a much more balanced CB duo that can deal with almost any type of defensive threat, rather than opt with Martínez next to de Ligt, a duo that doesn't have enough pace, and often not enough height either.