If Power and Callan are both the same in terms of being fringe players (and I rated Power more highly than most), then getting pick 48 for Power, and only downgrading pick 62 to 66 to get Callan seems a decent win.
I'm not sure it is as simple as this but Callan's purported attributes (defensive, hard-at-it) are something we need. I however, still thought Power had a chance of becoming a damaging player for us and would've liked to have them both.