I think HuGo saw that Montreal had the following on D:
Matheson-Savard
Guhle
and Kovacevic, Barron, Xhekaj, Struble, Harris (remember that the Laine trade hadn't happened yet), Hutson, Mailloux, Reinbacher and Engstrom (plus I guess Trudeau, but no one was talking about him).
I don't think it was about any one player or another, its that they had a shit ton of young D that hadn't established themselves or shown that they could be more than a bottom pair D. Trading the oldest guy who was a year away from UFA status made the most sense at the time since no one would have predicted his trade value to skyrocket. And Savard's game falling apart was frankly the bigger issue than anything else: Barron was traded for Carrier, Hutson should win a calder, Struble showed growth and Xhekaj has an element to his game that no one else on the team does.