The biggest challenge I see with the Derricot kid is how fast he's able to actually learn his roles in the defense and develop chemistry with the others.
It doesn't matter how fast or skilled a kid is, if he doesn't play within the framework/scheme of the defense, he'll leave holes exposed and a bunch of internet bloggers that don't get it will blame the problems on other less athletic players because they won't be able to make up for his errors.
I agree 100% with the chemistry aspect of this whole deal. If he doesn't fit in and mesh well with the rest of the D, then we have problems as you listed above. To some extent though, when the rest of the D see's that he's a mean MoFo and hits like a Mack truck, then I think they'll be a little more welcoming and understanding that he showed up late.
It's not like he's been sitting around playing PS4 and eating cheetos all summer. He has a playbook and has been working out to shorten the learning curve once he's in fall camp.