Hindsight is easy, anyone can do it... but there were criticisms, at the time, of every trade Army made on that blueline. Unforced errors.
Even if we assume Seattle still yanks Dunn in the expansion draft this defense would STILL be better, IMO, with Edmundson still on there with Walman and Mikkola than it is now. At least we'd be younger with less cap restraints, if absolutely nothing else.