Those runs from LB have caught so many teams off guard when he just overloads and ghosts in. Whereas at CM, he just gets more marked by default.
This is partly why I see O Reilly's ceiling as a LB to potentially be "Best LB in the world".
And while I think he has done great at CM and has helped in some games shore us up defensively, and should definitely continue to play there for us there as well, his ceiling for me there is at best something like " Top 20", still very good but not quite worlds best potential.