I note your observations and agree with them especially the absence of another good anti-run Big Body like Siliga.
As to Kelley I was surprised when the Pats released him, only to find out he asked for his release. The ostensible reason is that he felt platooning with Easley was beneath him, and hurt his possible incentive pay. Certainly the Pats were going to give some snaps to their First round pick.
But he signed with the Cards for the exact same pay, minus any incentives, so that doesn't wash. If he stayed, he would have had the position and Vellano would have been consigned to the PS.
I can only hope that Walker turns out as well as Sealver did, in three or four games.