I'm fine leaving this up to Key and J. If Key wants to bring in a new guy, I hope J can authorize the budget for the guy(s) in Key's short list.
I see the same thing everybody else sees on the field but I still think this is a case of the coordinator taking too much of the blame for roster issues. One thing I have learned over the years is this - on D, the gap in the average talent level isn't what kills you - its the lowest talent level across all 11 positions. So, you can have a D with a lot of great players but even one or two guys that are grossly overmatched is all it takes to swing the outcome of the game.
A top-shelf DC can sometimes scheme around "holes" in the roster but they other team's OC will, over the course of 4 quarters, find the well-disguised weak spot and, as O'Leary brilliantly put it, "make you play left-handed."
The dwags final (meaningful) 3rd down conversion illustrates exactly this. We called the exact right D - literally the perfect call. But we ended up with a matchup not in our favor and they converted. If we had the LB duo we had last year, we would have forced a punt and had one more shot for another score.
So I think we need to focus on fixing the root of the problem. Not that a better chess player running our D would be a bad thing but the problem seems to be we need more rooks and bishops and fewer knights and pawns.