If Vick, Floyd and Juice were all mediocre like Kaep, I believe they would have received the same treatment. Honestly, I don't know anyone who doesn't think OJ is a scumbag.
Ray Rice could've been a #2 back for a couple more years on some teams, but at that point his mediocre play wasn't worth the hassle. If Kaep was a top 20 QB he'd be on a roster.