You are correct he was a good player but not number one on that team. It seems he was a good blocker and for sure was a burner but he seldom got the ball in space. He had problems with fumbles on pitches but that was not always his fault.My guess is that Snoddy's overall body of work stands out in the statistical areas important to PFF's grading system. If you look at his numbers here: https://www.sports-reference.com/cfb/players/broderick-snoddy-1.html, which does not include the blocking metric that PFF also uses, they are fairly impressive. The fact that his carries were split a lot with others in the A-back role makes it seem like he wasn't an impact player.
Ave yards/carry: 7.8
Ave yards/reception: 25.2
KR ave: 22.4
Different system, but those stats arent too shabby.