I ask anyone critical of Knighton to Rewatch just the first series of the 49ers pre season game.
The very first play he would have had a TFL, but Ayers drove across the formation and allowed Little James to bounce the play outside.
He frequently drew double teams, showed the ability to anchor and shed. He certainly isn't the pass rusher Jackson is, but Knighton made his way in the backfield several times.
I didn't see anything disappointing from the limited body of work that we watched.
I don't see how you keep Unrein over Knighton.