Kounde, Thiago Silva and Koulibaly would be a good back three. It's not particularly better than Azpilicueta/Christensen, Thiago Silva and Rudiger though and age profile wise it's similar (Kounde is younger than Azpilicueta but Koulibaly is older than Rudiger). It's a lot of money spent to pretty much stand still and I'll only be convinced by Koulibaly in a back three once I've actually seen it.
Similarly up-front where they've brought in Sterling but loaned out Lukaku and imminently Ziyech.
I'm guessing this may be the new owners one big splurge transfer window and so far it's all a bit meh. They still haven't managed to find a taker for the world's most expensive goalkeeper or Werner either, probably because they overpaid for both and put both of contracts no other club will get close to matching.