I'm Brazilian and I've been following Newcastle transfer window. Look, in my opinion the great defender of Sevilla is evidently Koundé, much more sophisticated than Diego Carlos. What Diego does well is complementing Koundé with a more assertive and aggressive posture.
Will he work at Newcastle as the team's main centre-back? I think so, he is no worse than the players I watched against Watford.
Is he Newcastle's salvation? No. It would be nice to complement Diego with a player like Botman who, in addition to being tall and strong, also knows how to play with his feet, Diego is a more of a "traditional" defender.