Despite the injuries, the defense hasn't been the issue in this series. None of the forwards can hit the net if their life depended on it. You have Pastrnak, who looks like he hasn't played hockey before, Marchand who is dipsy do-ing all over the place, and Bergeron who looks like he forgets what a face-off is.
Being built for the playoffs isn't the issue. You can't win a game when your scorers aren't scoring.
Besides Chara at the end of games after playing ~30 minutes, and Cross, who, c'mon, is a 10th defensemen, our defense has been pretty good. Our lack of speed is evident, but guys like Morrow, Killer, and McAvoy especially have really stepped up. Every game has been a one goal game... You're right, defense is NOT the issue. Still, having Carlo would likely improve our PK, which would be good enough to win at least one more game. Krug is more important to our offense than all of our forwards except Marchand, Bergeron, and Pasta, I think. With all of them struggling, and us struggling to pass tape-to-tape, he's been invaluable. But given the situation, our D has been great and that makes me confident moving forward.
Marchand, Pasta, Bergy, and Krejci in particular need to start scoring. If they do, we can take this series. But all of them are struggling big time. They have no space out there, and 63 and 46 in particular are turning the puck over like there's no tomorrow. Pasta has also resorted to bambi legs, like his rookie year. That's not like him.