So I just finished watching the Oklahoma game....
Sooners OL dominated TCU pretty much all day, so I think that heightened Summers' biggest flaw which appears to be mental processing/reads. Once Summers knows where to go he's on it. But his play is hesitant while still reading.
Summers never came off the field, so I'm not sure why scouting reports said he came off during passing downs. He covered WRs and RBs. If he was covering a RB he pretty much took him out of the play. Kyler Murray only attempted a pass in his direction but once, and that RB got creamed for an incompletion by Summers and another LB. For coverage on WRs Summers was never step for step but for the NFL, they would be considered open. However in college, even with the #1 Overall Pick throwing the ball, it would be discouraged throwing in such a window.
In an odd scheme or sub-package front where Summers is playing ILB alongside Martinez, I would definitely assign Summers the cover job. In the NFL I doubt Pettine will ever ask him to cover a WR, outside of the defense getting stuck in a hurry-up tempo where it's hard to make a substitution. OR make him the designated pass rusher until he can get his processing hopefully up to par. He plays SOOOO much faster when he doesn't have to make too many reads. He was a defensive captain for TCU so maybe taking away that added responsibility frees up his brain so that he can just play.
I might watch the Oklahoma State, Kansas, or California games where the teams are a little bit more even. Sooners just basically did chunk plays all game. The TCU defense was essentially powerless despite making stops here and there, plus TCU has a QB problem(of which I was unaware) so Summers and the defense hardly got any rest either.