I wouldn't pretend that ypc is irrelevant. I mean, only three running backs (min 150 carries) ran for sub 4ypc in 2013 and 2014; they are Steven Jackson, Trent Richardson and Joique Bell and only one of these guys has a job atm.
Still, Bell has been all around very solid for DET which is why I can understand their attachment. He has showcased a 3-down skill set (good in short yardage situations, good pass blocker/catcher). He lacks true play making ability but that's why they brought in Abdullah.