While I've only been keeping half an eye on our potential transfers, I'd be worried about signing any "not the finished article" CBs. If we end up playing a back 4 with Udogie / Sess / Reguilon at LB and Royal / Spence at RB, we need a solid LCB to partner Romero. If it's going to be a 5, we need an experienced CB to lead the line flanked by Romero and Davies (?).
We've clearly had a shaky defence for the last couple of seasons, regardless of how much blame you apportion to managerial tactics. Dier and Lenglet aren't the answer, I'm not sure how long Davies has left at this level, and I just can't see us having the time to bed in another youngster in such a key position.