Much of the same was said last year when the Pau Torres rumors surfaced. We had Mings and Carlos who could both play in that position, and the money was needed elsewhere. Mings was injured, but Torres was bought in before that, because he was an important piece in Unai's way of playing football. If you want to build a good team, the defense must be in place, and this season we have let opponents get in front of our goal all too easily.
Now I also don't think we will pay 70m for a defender, but might as well use the money there. Although I agree that the need for a midfielder is greater.