When I watched Sims last year, I would see many plays where Sims would be a half step late getting there, missing possible interceptions by a half step, being a little out of position...and he still led the Lions in tackles. The Lions defenders had a learning curve with the Tampa-2 defense, and it was even more magnified for Sims because he was a rookie. He should make a lot more plays this year, both tackles and big plays because he has a year in the Tampa-2 defense and now can react more and use his instincts, instead of taking that extra second to think about what to do, as he did last year. He is a perfect fit as a Tampa-2 WLB.
I see Sims having top 10-15 upside this year, and a definite top 10 caliber LB long term.