Not unusual for bigger backs to need reps to get going.I think he’s right about Mangham needing to find a rhythm. Problem is there aren’t enough footballs to waste while he finds that rhythm and Broussard only needs two or three carries before he goes beast mode.
Also, it can be very effective for the rotation at RB to be different styles. Defenses also get into a rhythm, so when a RB comes in and brings a different pace to the same play it can keep them off balance.