The trend we keep seeing over and over again is this: we seem to dislike young defensemen, and we would rather play veterans. We never took Dunn off of the leash, even though he deserved it. We barely gave Walman a chance. We didn't give Schmaltz a legit shot until his D+7 year, and then promptly traded him for Andreas Borgman (who we also did nothing with). We sent Kessel down in a year that was supposed to be a "retool" instead of letting him take his lumps.
The problem is what we can call the Krug/Faulk problem. We spend all of this capital on getting older defensemen with polished games, and pay them a bunch of money on long-term contracts. When they (predictably) start to fall off a cliff, they still have several years left on their contracts. At the same time, we have young guys maturing and ready to start taking on roles, but they're blocked because you can't cut/healthy scratch a $5+ mil player. So we waste their prime years, and then by the time we're ready to cut bait, their value has fallen and we don't get great value out of them. And so now we don't have a backlog of competent dmen, so we have to go out and sign/trade for a veteran, and the cycle continues.