Up front, I don't have a problem with how they are built. At least in theory. They have top end skill surrounded by a good mix of skill (Guentzel, Simon, Cullen), speed (Rust, McCann, Blueger), and big bodies (Hornqvist, Pearson, Bjugstad, ZAR). Pretty much everybody is responsible defensively (at least when they want to be in Malkin and Kessel's case) and at least not totally worthless offensively. With that group, I think they can play pretty much any style depending on the opponent.
Where they are struggling is puck movers on the blue line. I think it would be exhausting, physically and mentally, to put so much work into helping the defensemen get the puck out of the D-zone and by the time they do, they are near the end of their shift or the opposition has enough guys back that entries are difficult. Then they gotta dump the puck in and do even more work to get possession. I think their forwards are good enough that they CAN do it, but over the course of 82 games, they just don't have it in them every night.
Missing Schultz for basically this entire year has been a huge factor and never replacing what Daley brought has hurt the 3rd pairing. I've wanted another puck mover because of how much time Letang and Schultz miss and how much the team struggles without them. Without knowing how Schultz is going to come back, it's even more of a need IMO.