You don't have to be Hall of Fame level to be dynamic or impactful. It just so happens that CMC is Hall of Fame caliber.
Swift is an all purpose guy that can also run between the tackles and Montgomery is perfect for what Dan Campbell is trying to accomplish. They fit in the schemes their teams are running. That's more important than anything.
The Bills, to me, don't have an identity on offense outside of Allen to Diggs. Ken Dorsey sucks, so it doesn't matter who's carrying the ball here.
*On a side note, it is my opinion that Beane really wanted Montgomery in the draft, but the Bears pounced first and we ended up settling for Singletary.