Really? I think he's been doing quite well on trades recently. With the possible exception of the Gudbranson trade I don't really see any huge misses.
He's blown it on pretty much every big trade outside of the Shinkaruk-Granlund, Baertschi-2nd, Dahlen-Burrows, and Bieksa-2nd. Half of those trades the other team approached the Canucks and offered the asset without much negotiation taking place (Ottawa offered Dahlen for Burrows, and it can be presumed that Anaheim offered a 2nd for Bieksa).
Which leaves the following trades that Benning has botched:
Vanek
Forsling
Gudbranson
Sutter (Bonino alone should have been enough)
Kesler (could have gotten a higher quality asset back rather than quantity)
2nd for Vey
5th for Larsen
Jensen and a 5th for Etem
Kassian for Prust
Garrison is arguable
Neutral trades:
Hansen (not looking good for either team right now)
Pouliot
Leipsic (too early to tell, but it looks decent)
Subban for Dowd (too early)
As you can see, much more bad trades than good trades. And the bad trades have had a substantially bigger impact than the good ones (McCann and 33rd overall for Gudbranson; Kesler for pennies on the dollar; Forsling for nothing; 2nd round pick for Linden freakin Vey, etc.).