Little column a, little column b.   Barkley has had multiple leg injuries and it's fair to question if he's the same back as he was when he was elite.  Adding another on top this year doesn't make me any more favorable towards his outlook.
Add to it that he simply hasn't been able to stay healthy for a solid stretch of time... Sometimes being able to stay on the field is a skill onto itself.  Even if he comes back with the same form as his rookie year, he's still a higher injury risk than others at a position with a high level of injury risk.  Anointing him as a solid rb1, let alone a potential top 5 like 
@travdogg among others have, fails to 
bake in all the inherent risk that Barkley comes with.