I think people saying "the primary issue with this team is they're old" and "the primary issue with this team is that the supporting cast is not good enough" are saying basically the same things. The problem is that the core is old and worse than what they once were, and the support cast is not nearly good enough to make up for that. Both are true. It's not really a blame game type of situation here, it's just rightfully pointing out the situation of their team.
Malkin's a 65 point 2C at this point. Crosby still a PPG 1C, but a "PPG 1C" at this point only has him as a top-30 player in the NHL today, not a top-10 player. Letang is still a good top pair D, but he's not even close to a top-10 defenseman anymore like he used to be. They need a substantially better supporting cast compared to what they used to need to make a competitive team today.
No star can carry a team that insists on playing hockey that isn't all suited to its roster. Yes, if Sid and Geno were younger, the team would be better, of course but it would still be a colossus with feet of clay because it's playing a deeply stupid brand of hockey and no amount of individual brilliance can make up for that. Especially in a league with so much parity where refs try so hard to help scrubs stop superstars.
Why was this team successful with Sullivan's system 5 years ago but not today?
Yes, the team today is not suited to play Sullivan's system anymore. But to say that a younger Penguins team wouldn't be successful with Sullivan's system, when a younger Penguins team was successful with Sullivan's system in the past, seems like a bizarre thing to say.