As in Javi Martinez style, being equally worldclass as DM or CB, or more like they can, but they should not, if avoidable ?
I think it's harder to be a world class full back and centre back in the modern game. Thuram is the last person I can think of who could do both.
Saliba and Hermoso are more like Vermaelen and Vertonghen. Capable defensively but don't give you much going forward. You are not getting past Saliba though. He can put wingers in his pocket.