Key defenders can always be traded.There is a reasonable chance that Gibcus will be available when we exercise our pick #5 (assuming this remains our first pick). Could do worse IMO. The weight of opinion on this site is that we should target quality mids but I would be comfortable with Gibcus, Andrew or Rachele. Hartigan has at best a couple of seasons left and Frost 3-4 so Gibcus would be a good strategic acquisition.
Mid's would be a lot more valuable, with our current absence of young, promising gun mids.