It wasn't neccesarily that last years WR's core was better. It just had pieces that complimented each other. Having Ginn and Smith's savy made last years offense more vertical than this one was.
This years squad has too many guys of the same skill set. Cotchery, Avant, and Bersin are players that serve the same function. Philly is decent, but he's young and it's a lot to put on a UDFA to beat Richard Sherman on a go route.
Had we kept Ginn and Steve Smith to team with KB we would have hell of a WR core. You'd have the always open redzone guy in KB, the deep threat who gets yards in chunks with Ginn. And finally Steve Smith to make the clutch catches with YAC ability.
Right now we just need a guy with hands and speed.