I think it's a fair point about Barron and how last year he was probably their worst defender (plus health issues). So the gap between him and Kiser probably isn't that much, and Kiser likely develops in year 2 with starter reps in OTAs, camp, etc.
I will say I think with Sullivan it wasn't that he was bad all year but that- for the 2nd straight year- he wore down as the season went on. I think he was actually very good through the first 9-10 games and then started wearing out rapidly from there. He got abused vs. Chicago and Philly.
