The offense and it's approach to getting Sammy the ball is so f***ed up, it is hard for the blame not to be shared by all parties involved. Watkins, his injuries, Manuel/Orton, bad OL pass blocking, OC & playbook, playcalling to Sammy or lack thereof, & the HC Marrone.
Regardless, they are looking like fools for giving up what they did to get Watkins, and then have him be outperformed by Beckham, Benjamin, Evans, and to some extent, even Landry and Matthews could be argued.