Jack has a few flaws but not many so Sturm is right on with his analysis.
Further, size is not one of them even if they play him at MLB he is currently 245 and ready to go (the knee injury has healed and was not an ACL), the NFL has changed and covets linebackers that can do it all, plus Eberflus loves linebackers with flex specifically.
It is valid to say that his inexperience with only 25 college games under his belt could be part of the evaluation and perhaps poor coaching and lack of specific allocated placement could cause some pause.
Intelligence is not a factor, he is just young in linebacker years and Sean Lee and Eberflus can help in this area but his ability is off the charts, you can not teach his play making ability and natural instincts.
However, as Dane Brugler argues, these concerns, although valid, do not overcome Jack's skill set and play making/athletic ability to be an impact player on the next level.
Many have Jack as a top prospect for this reason, some as the best player in the entire draft class and others in the top 5 for worthy consideration.
I love Jack as a top five prospect but I covet that franchise QB primarily, however, if they go defense, Jack and Lee will make a hell of a team and will make difference!