Krug's main issue in last year's playoffs was being paired with Miller, because he lost Carlo. No Carlo meant Krug had more touches of the puck, more responsibility on break-outs and transition, increasing the fatigue factor significantly. Carlo may not produce points but he can pass and he can skate.
The last regular season game in Toronto, the first TO goal was all on Miller, he was pressured in his own end, threw the puck right up the middle, and it was picked off, zone possession maintained, and they scored. His next shift, he made another turnover in his own end, then took a penalty to stop the scoring chance, and they scored again.
Between Miller (or Chara for that matter) and Krug, which one would the opposing team want to handle the puck more? The better decision-maker in Krug? I don't see it.