Tbh with 16 yo kids I'm not as worried about where (what position) they play but more on how much and how they play. I know you can't perform to your best if not on your ideal position but it's not like we'd ask him to play in a totally new position like a CB he has never played before (I assume).
We don't need to define his position now and being versatile is always good to get minutes one way or the other. Just get him on the pitch and earn experience on a higher level he has played so far. Depending on form/availability of other BA players Marquez can use him in multiple positions.
We don't know what ambitions he has and what plans the club has presented to him (might be they promised him easier path to the first team based on recent examples of likes of Ansu, Gavi, Pedri and Yamal so he decided to come here rather than going to clubs whose offers were probably better from a financial standpoint) but he's only under contract until 2026 so both Barca and Darvich will have to make a decision over next two years anyway. Either renew and keep him at the club (loan ofc an option as well if they decide that's the best) or sell with buy back which we're doing nowadays with players like Nico, Chadi Riad,...who could potentially still have a longterm future at the club but are not ready yet. Ofc he's younger than them and also not homegrown so he might not want to return after leaving though.
But first thing first I think we should give him few months to fully adapt and then see if Rafa will give him a bigger role. I think he has higher ceilling than likes of Aleix Garrido (who I also like) but is understandably not as developed nor as familiar with the system yet.