Yeah, strokes and concussions will do that to you (see Crosby Sid, for the latter). The guy has still put up the 2nd highest point total amongst defensemen in the last 3-4 years, and despite logging huge pp minutes is still amongst the league leaders in even strength goals.
Labeling Letang any as a liability after this season is a mistake, he's way too young and talented, you don't write off guys a year removed from being a Norris trophy finalist, especially considering what he went through. I think most people recognize that, at least they should.
Geez, I don't even like Pittsburgh.
Norris trophies are largely driven by offensive production, not defensive prowess. He's been waning for years in addition to not being able to stay on the ice.