Think he’s a good fit for Frenkie. Good long range passing, better in physical duels than him. Frenkie better at carrying the ball.
Anyway, looking at the names we are linked with Frenkie, Gundogan, Pedri and Gavi will be the core formation.
He plays differently to FDJ, but he occupies same space as the Dutch.
That said, with the way we play I think we can afford different types of CDM tbh.
We play a hybrid gameplan, that can be 433, or 343 (3223) or 442 depending on the individual and opponents.
Our midfielders are Pedri, Gavi, Kessie, FDJ & Gundogan (hopefully) and they all have different profiles and styles.
This allow us to be able to afford a different DM, and mold the team in a way that fits him. Essentially choosing quality over fit.
Diaz could fit like that in a double pivot where he and FDJ exchange positions, think when we played 3atb under Koeman with FDJ as Libro and Busquets/Pedri as double pivot. Can see something like that with FDJ and Diaz. Such combo won't free Frenkie tbh but won't restrict him too much either.
We can also afford a destroyed type and let Frenkie, Pedri, Gundogan be our outlets to get the ball from the back, instead of CDM. And obviously a CDM like Kimmich/Zubi as Busquets 1 for 1.
The big question is this, is that the way the club/Xavi thinks? If it is the case then getting someone like Diaz makes sense, if we are hell bent on the last type then Diaz would get the Torre treatment if he joined.