Honestly, though - how weak is our D corps (if we tried to remove all bias)? I know that is near impossible. If I am trying to be completely honest, this is my assessment:
Morrissey - Poolman: Morrissey is barely keeping his head above water right now. He is making uncharacteristically poor plays (yesterday he ended up biting bad on a fake and actually fell towards the boards during one play. I think he is struggling to be 'the guy' on the first pair with a partner like Poolman, who we can all agree is not ready for, and will likely never be ready for first pair duty. Buff back and on that pair instantly makes it one of the best 1D pairs in the league.
Sbisa - Pionk: Pionk has easily been our best defenseman this year. So much so that I think he is making Sbisa better too. Sbisa has been much better than advertised, but I think the overwhelming negative bias for him is making it hard for people to accept that (though it is changing). Sbisa does have his limitations (quick thinking and positioning defensively at times) but he is a surprisingly well balanced player. He is tough and physical, nice size. He has a cannon for a shot and pretty good instincts. Overall, this pair has been our best and I think stacks up pretty well against other second pairs in the league.
Beaulieu - Bitteto: The problem with this pair is that Beaulieu has not played enough to get into a groove, and Bitteto, though an adequate 7th guy filling in on spot duty or maybe drawing in for more physical games, needs a better partner to help him. We do tend to get hemmed a bit in our own zone with them on the ice, especially when our fourth line is out there. Kulikov with Beaulieu would be much better (but I don't know if either of them are comfortable on the right side)
Trying to be as unbiased as possible, and limiting my fanboyism and optimism, there is obviously significant room for improvement here. However, getting Buff back and adding Niku gives us so much more options and in my mind quickly transforms this D into a high middle corps stacking up against the other teams in the NHL.
If we can get Buff back, and use some of our (hopeful) cap savings from his absence towards getting a D rental at the TDL - this team could really take a run in the playoffs.