Discussions of comparisons aside....
This is ignoring how he was used at Ohio. You can't complain about Edelman's yards per catch, when he's used to get 1st downs for that offense.
Campbell, as has been pointed out by PFF, was NOT targeted downfield despite his "speedster" status. He is indeed blazing fast, but they used McLauren in that role. I think Campbell only had a handful of downfield targets. He was basically used on crosses and hitches - yards per catch is irrelevant in this discussion.