It's kinda hard for me to take Yohe's comment of "their depth is a problem against good teams" seriously when Malkin's line is once again barely breaking even at 5v5 this year. Here are the 5v5 goal differentials of their centers this year:
-Crosby: 21 GF, 13 GA
-Malkin: 11 GF, 11 GA
-Eller: 7 GF, 6 GA
-Acciari: 3 GF, 4 GA
The bottom-6 isn't great, but it's doing its job: breaking even while eating tough defensive minutes. The Penguins have a 9-8 goal differential without Crosby or Malkin on the ice, it's not anything stellar but it's solid. I think the 4th line has had issues but I think the 3rd line has been notably good.
The reality is that this team is built based on the idea of "the top-6 wins them game and the bottom-6 doesn't lose them games". Crosby's line is doing its part in the top-6 and both of the bottom-6 lines are not blowing games. It's Malkin's line that isn't carrying its weight at 5v5.
I'll note that I don't think this is due to Malkin, but Malkin has been notably bad in each of their last 2 losses. He was amazing to start the year but has seemingly really come crashing down.