There does seem to be some systemic issues but it's hard to tell what is system, what is players not executing properly, and what is just the fact that this isn't a good hockey team yet.
I feel like there is a lot of execution issues that are coming from players just not being able to process the team game at full speed right now. When they face a team that doesn't pressure them as hard like Buffalo, they have a bit more time to make the right play, be in the right place, etc. When they face a team that is moving faster and more aggressive, guys start panicking, start losing their marks and their places on the ice, get confused, get behind the play, etc.
Is it bad players? System? Execution?
Probably all three but I've seen even bad teams in the NHL put together respectable defenses by just playing a more simple and conservative game. ON the other hand that means then we all get to complain about the offense being too vanilla and not letting skill players do their thing, etc etc.
My biggest complaints have been that teammates aren't supporting each other very well and are forcing each other to have to win outmanned battles along the boards, make difficult and long passes when they do have the puck, etc. When forechecking and trying to start a cycle, you need support in close, not one guy standing in the slot and the other guy behind the net and the D standing outside the blueline. The forechecker gets easily overwhelmed and out numbered and then it's back the other way. The incredible thing is that this also means an easy breakout for the other team and often traps the other forwards deep...they're not even helping forecheck, but they're stuck deep after the other team breaks out, and then the D have to conceed the blueline because they have no help coming.
similar stuff in the defensive zone, often the support isn't there and guys start getting confused as to who to cover and what to do
So, I dunno, I think there are a lot of parts to this that are badright now and the hard part of stripping the team and moving so many players year after year is that it breaks down the overall structure and you're left with a few guys from the days when the team used to function, a ton of kids, and a handful of new vets who aren't familiar with anyone either.
A team like Boston has basically had the same vet structure in place for years and they don't have to relearn everything every season.
So, I dunno, I'd be happy to fire Ruff because I think he's bad at his job no matter what but it probably doesn't immediately make things better either.