I just don't get how you single out Martin and Michalek there. They aren't the only D getting scored on. They're no more to blame than Letang and Orpik are. It's interesting that the only D that were pluses pretty much were the guys that didn't play many minutes and didn't have to play against the top guys. Michalek actually was a +2 in the series. Like I've said recently, what seems more likely, that the entire top four forgot how to play D or the team's style of play isn't suited to strong defensive hockey.
I'm far from an X's and O's guy, but what I understand of Bylsma's hockey is that defensively the strategy is to get the puck out quickly, get the transition going, get the puck into the other team's zone, cycle, get pucks on net, and wear them out. The problem is what happens when they don't get the puck out, they just seem to do a lot of running around in their own end as a team, guys miss assignments (including forwards) and bad things happen.
The problems I see with the team are three folds. One, there's not enough D structure. Other teams seem to be able to do a masterful job of closing shooting lanes and pushing the Pens to the perimeter for low percentage shots. That was the theme of the 2010 Montreal series and Philly did a good job of locking down like that to protect leads. The Pens had no capability of doing that, their only style was to play "their game" regardless of the situation. Another issue is that for Bylsma's hockey to work, guys have to be playing smart, focused, disciplined hockey. Everyone has to be on board. One guy makes a mistake and everything starts to fall apart. How many times did you see a D, Letang and Martin in particular, get caught pinching with no one backing them up leading to a two-on-one or breakaway? Too many system breakdowns and as I discussed in another thread, I think a lot of that comes down to guys being allowed to get away with mistakes all season without consequence. Finally, as we've discussed a lot, no adjustment. It seems that in all areas, the Pens get figured out and they have no answer to it. Philly gets down early in games, they make in game adjustments, and they take over.
In other words, replacing the defensemen and playing the same way isn't likely to get you better results. This team needs more order and discipline. I think they need a system where D is the foundation rather than offense. As others have mentioned, it's probably not a coincidence that Bylsma had his most success when he inherited a team that was forced to be disciplined and play defensive hockey. He took that and opened it up a bit. Since then, other teams have scouted the Pens and figured out their tendencies and Bylsma has allowed a lot of that discipline to wear off.