The secondary, outside of Kyle Hamilton, later on, Clarence Lewis, wasn't exactly stellar. Tariq Bracy kept getting burnt all too often, and while Shaun Crawford was able to use his brains and experience to get in the right place at the right time, he often times lost the battles of athleticism (much how Joe Schmidt was in 2014).
Even though Brian Kelly had recruited good talent at the CB and S positions, the fact that a 6th year Shaun Crawford who was but a shell of his former self (he was physically outstanding in practice in 2015 before those injuries) was our starter at strong safety shows that we had some issues there.
That being said, I do staunchly agree that we need to really step it up on offense if we want to hang in there with Clemson, tOSU, and Alabama, on a regular basis (and not just a once in a long while upset). Going from top 10 material to top 3 is going to require that we truly stretch the field. Last year, we had a QB who was accurate with his short and medium range throws, and could also run the ball very effectively, which unlocked about 75% of the total playbook. Unfortunately, there wasn't much of a deep threat due to Ian Book's arm strength, as well as the fact that we didn't have a bona fide WR who could present that deep threat. The ones that could have were either injured (Lenzy, Keys), or benched (Johnson).
I think Javon McKinley and Ben Skowronek did a decent job as WR1 and WR2, but neither of those two had the ability to separate from their defenders and turn a short passing play into a long chunk gain the way that a Will Fuller, Chase Claypool, or even Miles Boykin, could.