Seeing as the Habs would be dumping Alzner's terrible contract on the Hawks, that doesn't seem outrageous to me. I mean, Alzner still has 3 years left on his deal, at only about a million less than Keith. So for 3 of the 4 remaining years on Keith's deal, you're basically offsetting that caphit. And given that Alzner is essentially playing at a fringe NHL level at best right now, i'd feel pretty confident even a 35+ Keith is going to be a significantly better player for at least a few more years. Right now, he'd be a plenty solid complement to Weber as a top-pairing LHD for at least this year and at least one or two after that, unless he absolutely falls off a cliff.
Really comes down to just how valuable you think Poehling is i guess. Compared to a couple years of decent complementary top-pairing LHD for the salary you're currently wasting on an AHLer in Alzner.
Or really, it's just a question of where the Habs should be headed philosophically. Whether they should bother competing in the now, or just focus purely on the future. A case where i think a lot of fan conceptions on here may differ from team ownership and management's ideas.